US3798842A

US3798842A - Long-arm grinding machine

Info

Publication number: US3798842A
Application number: US00147732A
Authority: US
Inventors: R Seybold; E Evertz; S Stadler
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-08-12
Filing date: 1971-05-28
Publication date: 1974-03-26
Anticipated expiration: 1991-03-26
Also published as: NL7109392A; GB1348166A; LU63448A1; BE769539A; FR2101533A5

Abstract

This invention relates to a long-arm grinding machine having an elongated shaft, one end of which is provided with a grinding head and the other end is provided with a motor. The elongated shaft is adapted to be pivotable by means of a tubular shaft bearing on a machine frame of the grinding surface width. The elongated shaft is also adapted to be slidable in the direction parallel or substantially parallel to the central position of the longitudinal axis of the elongated shaft over the griding surface length. The shaft bearing may be pivoted by means of an eccentric drive and is linked by levers to a pivotably supported ratchet support which in turn supports a ratchet lever having two oppositely constructed ratchets which can be changed over into a separate stable position at each end of the grinding surface length. The ratchets are adapted to entrain a ratchet wheel in the same of two opposite directions until a traverse has been completed in that direction, the ratchet wheel being also a component of a feed transmission whose immovable element is fixedly joined to the machine frame.

Description

United States Patent 9 Seybold et al.

[ Mar. 26, 1974 LONG'ARM GRINDING MACHINE [22] Filed: May 28, 1971 [21] Appl. No.: 147,732

[30] Foreign Application Priority Data Dec. 23, 1970 Germany 2063410 Aug 12, 1970 Germany 2040060 [52] US. Cl. 51/32 [51] Int. Cl B24b 7/02 [58] Field of Search 5l/32, 34 R, 34 H [56] References Cited UNITED STATES PATENTS 1,528,624 3/1925 Mannering 51/34 H 1,564,574 12/1925 Hunt 51/34 H 1,881,839 10/1932 Monson 51/34 H 3,126,673 3/1964 Marker et al. 51/34 H Primary Examiner Qthell M.- Simpson [57] ABSTRACT This invention relates to a long-arm grinding machine having an elongated shaft, one end of which is provided with a grinding head and the other end is provided with a motor. The elongated shaft is adapted to be pivotable by means of a tubular shaft bearing on a machine frame of the grinding surface width. The elongated shaft is also adapted to be slidable in the direction parallel or substantially parallel to the central position of the longitudinal axis of the elongated shaft over the griding surface length. The shaft bearing may be pivoted by means of an eccentric drive and is linked by levers to a pivotably supported ratchet support which in turn supports a ratchet lever having two oppositely constructed ratchets which can be changed over into a separate stable position at each end of the grinding surface length. The ratchets are adapted to entrain a ratchet wheel in the. same of two opposite directions until a traverse has been completed in that direction, the ratchet wheel being also a component of a feed transmission whose immovable element is fixedly joined to the machine frame.

20 Claims, 8 Drawing Figures PATENTEU MAR26 i974 SHEET 1- BF 4 FIG.1

PATENTEDHARZB mm 37298342 saw uor 4 I LONG-ARM GRINDING MACHINE This invention relates to a long-arm grinding machine, and more particularly to a long-arm grinding machine for the internal grinding of chill moulds. Such a machine has an elongated shaft, one end of which is provided with a grinding head and the other end of which is provided with a motor, said shaft being adapted to be pivotable by means of a tubular shaft bearing on a machine frame and over the grinding surface width, said shaft being also adapted to be slidable, approximately along the general shaft length, over the grinding surface length.

In such a system it is a disadvantage that the tubular shaft bearing must be guided manually to enable the grinding head to machine the entire grinding surface. This activity is strenuous even if the weight of the grinding head is substantially balanced by the weight of the motor. Moreover, it is not possible to eliminate irregularities resulting from the effective grinding period per unit surface area and therefore it is notpossible to eliminate irregularities in the rate of stock removal.

Attempts to automate this operation have been found to be too complex or too trouble-prone in the end result since the operating conditions are relatively rough.

It is an object of the invention to provide an improved long-arm grinding machine of the kind mentioned heretofore so that the previously mentioned disadvantages can no longer occur.

In accordance with the present invention there is provided a long-arm grinding machine having an elongated shaft, a grinding head mounted on one end of the shaft, a motor mounted on the other end of the shaft, a machine frame, a tubular shaft bearing mounted on said machine frame and supporting said elongated shaft for pivotable movement over the grinding surface width, means for permitting the elongated shaft to slide in a direction parallel to the central position of the longitudinal axis of the elongated shaft over the grinding surface length, characterised in that there is further provided an eccentric drive for pivoting the shaft bearing, a ratchet mechanism, a pivotably mounted ratchet support supporting said ratchet mechanism, and levers linking said shaft bearing to said ratchet support, said ratchet mechanism having two oppositely constructed ratchets which can be changed over into a separate stable position at each end of the grinding surface length, and which entrain a ratchet wheel in the same of two opposite directions until a transverse has been completed in that direction, said ratchet wheel forming part of afeed mechanism, and there being provided an immovable element fixedly connected to the machine frame for co-operation with said ratchet wheel.

With a grinding machine of this type it is possible for the motions of the grinding head both over the width and over the length of the grinding surface to be controlled with a degree of reliability which has been hitherto unattainable. The eccentric drive provides the pivoting motion and the feed in one pivoting direction, the feed being subjected to an automatic change of direction by the change-over of the ratchet lever after the grinding surface length is reached.

The shaft bearing of this machine is pivotable so that it is possible to perform an adjustment for different amplitudes. This can be achieved with particular simplicity by means of a coupling rod, one end of which is supported on the shaft bearing so as to be pivotable in all directions and the other end of which is supported on a crank circle so as to be pivotable in all directions. Moreover, a driven rotating disc, forming the crank circle, is provided with a bearing which in turn is pivotable about an axis extending through the link between the disc and the crank rod. In this apparatus it is possible merely by pivoting a bearing pedestal which supports the driven rotating disc, to vary the oscillation amplitude as desired between zero and a maximum value. The maximum value is reached if the disc or crank circle is moved, by pivoting of the bearing pedestal, into a plane which extends parallel to the coupling rod in any desired position thereof. It is, therefore, not necessary to shut down the drive if it is desired to vary the amplitude. v

In order to furthermore obtain a uniform velocity distribution along the displacement path and for each path, the eccentric drive is provided with a disc cam which controls a pin which is pivotably linked to the shaft bearing. A disc cam with a cardioid path of motion, a so-called cardioid cam is used in the event that a practically uniform velocity is required in the entire length of stroke. However, the velocity characteristics may be controlled in any other desired manner depending on the selection of the disc cam.

In order to obtain different lengths of stroke it would however be necessary to provide different disc cams and to exchange them in accordance with the required length of stroke. In order to avoid this necessity it is furthermore advantageous for the disc cam to be rotatably driven and for a slide to be reciprocated along its longitudinal extension through a cam roller which in turn is guided on a turntable and can be adjusted thereon and locked therein, a pin being slidable in a guideway which is provided in an arm which extends laterally from the shaft bearing. In the system the disc cam defines the velocity characteristics relative to the length of stroke. Rotation of the turntable enables the length of stroke to be varied within wide ranges, being sufficient to provide for an adjusting facility for the turntable over an angular range between 0 and A long-arm grinding machine according to the present invention will now be more particularly described with reference to the accompanying drawings wherein,

FIG. 1 is a general arrangement of one embodiment of the long-arm grinding machine in simplified form,

FIG. 2 is a plan view illustrating a change-over mechanism of a pawl lever which forms part of the machine shown in FIG. 1,

FIG. 3 is a cross sectional view of the mechanism shown in FIG. 2,

FIG. 4 is a side view of a crank drive for a long-arm grinding machine according to the invention, the crank drive being shown in its limiting position in which the oscillation amplitude is zero,

FIG. 5 is a simplified view of FIG. 4 in which the oscillating amplitude has a maximum value,

FIG. 6 is a plan view of a further embodiment of a control system for a long-ann grinding machine according to the invention,

FIG. 7 is a partially sectioned side view of the control system shown in FIG. 6 and FIG. 8 illustrates. yet a further embodiment of a control system for a long-arm grinding machine according to the invention.

FIG. 1 illustrates a grinding surface 1 which is to be machined by means of a grinding head 4 in two directions as shown by the double arrow 2 as well as in two directions as shown by the double arrow 3. The grinding head is driven through the intermediary of an elongated shaft 4a by means of the motor 5 which, in the interests of clarity is shown in reduced form. A hollow shaft bearing 6 is mounted on a disc 7 which in turn is journaled for rotation on a machine plate 8. The plate 8 is provided with wheels 9 by means of which it can be traversed on rails 10 mounted on a frame of the machine.

The disc 7 is provided with a lateral arm 11 which incorporates a guideway 12. A sliding block 13, which may be pivotally supported in different eccentric positions on a crank arm 14, is adapted to slide in the aforementioned guideway. The arm 14 can be rotatably driven uni-directionally about an axis 15 and such rotation of the arm 14 will cause oscillatory motion of the hollow shaft bearing 6 since the block 13 will act upon the arm 11. As will be evident selection ofa suitable eccentric position of the sliding block 13 on the arm 14 enables the oscillatory deflection of the disc 7 to be so adjusted that the grinding head 4 traverses over the entire width of the grinding surface 1.

The right-hand part of the machine as viewed in FIG. 1 shows a toothed rack 16 or the like which is mounted adjacent the rail 10 to co-operate with a pawl wheel 17, driven in the manner described above, in order to provide the feed motion. To this end, a shaft 18 about which the pawl wheel 17 turns is fixedly coupled to the machine plate 8. A disc-shaped locking pawl support 19, which supports the pawl lever 20, is supported inter alia on said shaft. A lever 21, acts on the locking pawl support 19, and the free end of the lever 21 is' hinged to one end ofa lever 21 at variable positions The other end of the lever 21 is pivotably supported at positions of the disc 7 which may also be varied. The angular range through which the locking pawl support 19 may be pivoted may be varied by appropriate selection of the lever pivoting points. It is thus possible with one motion of the locking pawl support 19 for the ratchet wheel 17 to be rotated by means of the oppositely constructed pawls of the pawl lever 20 by different amounts so that the feed which accompanies a pivoting motion of the disc 7 may be adjusted to a desired amount.

In the interests of clarity, the parts required for changing over the pawl lever are shown on an enlarged scale in FIGS. 2 and 3. These figures shown therein the pawl wheel 17, coupled to the shaft 18, and applying the feed in the manner described hereinabove. The locking pawl support 19 which is provided with the lever 20 is rotationally journalled on the shaft 18 above the pawl wheel 17. On one side, the disc-shaped locking pawl support is provided with a stud bearing 21 for the pawl lever 20. The two pawls 20' and 20" thereof are provided with inclined surfaces of opposite orientation so that the pawl teeth, not shown in detail, are entrained in only one direction of motion while the pawls slide over the pawl teeth in the other direction of motion. In the centre of the outer end of the pawl lever there is provided a bolt 22 which extends beyond the stud bearing 21, one end of a tension spring 23 acting on the bolt 22 and the other end of the aforementioned tension spring acting on the bolt 24 which is coupled to the locking pawl support 19. This gives rise to the ac tion already described.

A control lever 26 and an abutment lever 27 are journalled on a shouldered part of the shaft 18. Both levers are provided with radially extending abutment surfaces by means of which both bear on an abutment bolt 28 or both bear on an abutment bolt 29. This function is provided by the tension spring 30 which extends between bolts 31 and 32 provided at opposite ends of the lever. The operation described hereinbefore is performed by virtue of the force of an end stop acting on the abutment lever 27 near its end which supports the bolt 31. The end stops provided for this purpose are designated with the

numerals

33 and 34 in FIG. 1. The distance between these end stops on the machine frame may be adjusted to an amount equal to the grinding surface length.

The free end of the control lever 26 is provided with abutment surfaces 35 and 36 between which is disposed the bolt 22. If, due to operation of the abutment lever 27, the control lever 26 together with the abutment lever 27 bears on one of the

bolts

28 and 29, one of its two abutment surfaces 35 or 36 will push the bolt 22 and therefore the pawl lever 20 into one of the two stable positions. Since the pull exerted by the spring 30 is greater than that of the spring 23 and since furthermore the distance between the stop abutment surfaces 35 and 36 would not be sufficient in order to traverse the lever 20 with its bolt 22 into the other stable position, the pawls 20' or 20" entrain the ratchet wheel 19 in the same direction until the abutment lever 27 bears on one or the other of the two end stops 33 or 34 respectively.

Automatic control of the grinding head over the width as well as the length of the grinding surface is thus obtained in the manner proposed.

In FIGS. 4 and 5 one end ofa coupling rod is supported by means of a ball joint 102 near the circumference of a disc 103 which supports a bearing (not shown) for a rotating shaft 104 the end of which is provided with a grinding head 105. A grinding head 105 is arranged to machine the surface 106 which extends in the longitudinal direction of the shaft 104, the lateral boundary of the surface 106 extending in curvilinear form so that a different amplitude is required to enable the grinding head 105 to machine the entire surface 106. This is based on'the use of means illustrated by reference to FIG. 1 and permitting a feed orientated along the longitudinal extension of the shaft 104.

The other end of the coupling rod 100 is supported on the circumference of a crank circle represented by a disc 109 by means of a connection 108 which also comprises a ball and socket joint. The drive shaft 100 of the disc 109 is supported in

disc bearings

111 and 112, the other end being coupled to a motor 113. The

disc bearings

111 and 112 form the part of a bearing pedestal 114 which in turn is pivotable in a cup bearing 115 and a retaining bearing 116. The two

bearings

115 and 1 16 form a pivoting axis 1 17 which extends parallel to the plane of the disc 109 and through'the joint 108.

In the position illustrated in FIG. 4, rotation of the coupling rod 111 causes it to describe a surface which may be regarded as the external surface of a regular circular cone. To this end the ball joint 102- forms the cone apex of variable position. The oscillation amplitude in this case will therefore be zero. FIG. 5 shows the disc 109 in a position in which the bearing of the disc is pivoted through 90. This position corresponds to the normal crank drive. This provides maximum oscillation amplitude for the ball joint 102.

Means, (not shown) enable the rotational speed of the motor 113 to be varied so that it is possible not only to select a suitable variation of the oscillation amplitude of the shaft bearing but also of the oscillation frequency.

FIGS. 6 and 7 show merely a further embodiment of that part of the long-arm grinding machine which corresponds to the left-hand part of FIG. 1. The arm 11, extending laterally from the shaft bearing (not shown) and the guideway 12 provided therein can be seen. The sliding block 13 is adapted to slide in the guideway 12 and is disposed by means of a pin 51 on a slide 52. The slide 52 is provided with guide rails 53 on which the slide can be traversed on a turntable 54. A cam roller 55, which in turn bears under the grinding pressure on the external circumference of a cardioid disc cam 56, extends from the underside of the slide 52. The turntable 54 can be locked on a plate 57 and may be secured at different angular positions. The plate 57 is fixedly joined to the machine frame (not shown) of the grinding machine. The plate 57 also supports a motor 58 which drives the cardioid cam 56 through a shaft 59.

The example illustrated in FIG. 8 is based on an embodiment of the kind illustrated in FIG. 4. A cam roller 60, adapted to drive a slide 64 in a guideway 63 which is fixedly joined to the bearing pedestal 44 so that the slide moves perpendicularly to the plane of the drawings, bearings on a disc 39 which is constructed as a disc cam. The slide 64 in turn supports a pin 65 with a ball joint 61 on which a coupling rod 62 acts. The disc arm 39 is driven through a shaft 40,

bearings

41, 42 in turn being supported by a bearing pedestal 44 one side of which is provided with a bearing 45. In this way it is possible to select different lengths of stroke or oscillation amplitudes by pivoting the entire apparatus about the shaft which extends through thebearing 45. It is therefore also possible for this embodiment to provide a uniform velocity along tl'ie major portion of the length of stroke. By contrast to the previously described embodiment it is however not possible for the oscillation amplitude to be accurately reduced to its zero value but merely to a value near its zero value. By adopting an appropriate length for the coupling rod, the said deviation from the zero value may be kept very small so that it is thus possible to meet practical requirements.

We claim:

1. A long arm grinding machine for grinding a surface having a grindable width and a grindable length, said machine having an elongated shaft, a grinding head mounted on one end of said shaft, a motor mounted on the other end of the shaft, a machine frame, a tubular shaft bearing mounted on said machine frame and supporting said elongated shaft for pivotable movement over said grindable width, means for permitting the elongated shaft to slide over said grindable length in a direction parallel to a line defined by the longitudinal axis of said elongated shaft when said axis lies parallel to said grindable length and midway of said grindable width, characterised in that there is further provided an eccentric drive for pivoting said shaft bearing, a ratchet mechanism, a pivotably mounted ratchet support supporting said ratchet mechanism, and levers linking said shaft bearing to said ratchet support, said ratchet mechanism including a ratchet wheel and a movable pawl lever having two oppositely constructed pawls which can be changed over into a separate stable position at each end of said grindable length and which entrain said ratchet wheel in the same of two opposite directions until a traverse has been completed in that direction, and a feed mechanism of said machine, said feed mechanism having an immovable element fixedly connected to said machine frame for operative cooperation with said ratchet wheel.

2. A long arm grinding machine according to claim 1, wherein said eccentric drive includes a unidirectionally rotatable crank arm, a sliding block pivotably supported on said crank arm at any one of a number of positions eccentric to the axis of rotation of said crank arm, and a guideway which is formed in an element associated with the tubular shaft bearing and which is engaged by said sliding block.

3. A long-arm grinding machine according to claim 1, wherein said ratchet mechanism has a first tension spring means for retaining said pawl lever in two stable positions, said first tension spring means acting cen-- trally on an end of said pawl lever and being mounted on a position of said ratchet support which is disposed on a line projecting from the center of the end of said pawl lever and the lever pivoting point on said ratchet support, when said pawl lever is in an unstable central position between said two said stable positions.

4. A long-arm grinding machine according to claim 1, wherein said ratchet mechanism further includes a control lever means and an abutment stop lever means which have a common pivoting axis and movable ends distal from said axis, said control lever means acting on the center of said pawllever to drive said pawl lever into one of said two stable positions, and end stops for indexing said control lever means during movement thereof, said control lever means having a bearing which is independent of the appropriate position of said ratchet support.

5. A long-arm grinding machine according to claim 4, wherein a second tension spring means is tensionally disposed between said movable end of said control lever means and said movable end of said stop abutment lever means and which may be actuated by said end stops of the machine, said control lever means and said stop abutment lever means co-operating with abutment bolts which are mounted on said ratchet support to retain said levers in their stable positions.

6. A long-arm grinding machine according to claim 5, wherein said ratchet support, said control lever means and said stop abutment lever means are journailed on a common shaft which is fixedly joined to said ratchet wheel.

7. A longarm grinding machine according to claim 4, wherein said control lever means has two abutment surfaces which act on one end of said pawl lever, which abutment surfaces are disposed at a distance therebetween so as to provide said pawls with a limited clearance so that said pawls become detached from the teeth of said ratchet wheel when said ratchet support .changes' into an opposite direction of movement but without being detached during motion in an appropriate direction.

8. A long-arm grinding machine according to claim 5, wherein said second spring means tensionally disposed between the movable end of said control lever means and said stop abutment lever means has a tensile strength which is a multiple of that of said first tension spring means provided.

9. A long-arm grinding machine according to claim 1, wherein adjustable end stops are provided at both ends of said machine frame.

10. A long-arm grinding machine according to claim 1, wherein said shaft bearing is provided with a coupling rod means one end of which is supported thereon so as to be pivotable in all directions, the other end being supported on a crank circle so as to be pivotable in all directions said crank circle being formed by a rotationally driven disc which is provided with a bearing pivotable about an axis which extends parallel to the plane of said disc and through a joint between said disc and said coupling rod.

11. A long-arm grinding machine according to claim 10 wherein said disc bearing pivotal motion is adjustable and lockable.

12. A long-arm grinding machine according to claim 10, wherein said disc is pivotable in a zone between said plane extending parallel with said coupling rod means and a position in whcih the surface described by the motion of said coupling rod means forms a regular 1, wherein said eccentric drive is provided with a disc cam, and said shaft bearing is hingedly joined to a pin which is drivable by said disc cam.

17. A long-arm grinding machine according to claim 16 wherein said disc cam has a cardoid track.

18. A long-arm grinding machine according to claim 16, wherein said disc cam is rotationally drivable, a slide being reciprocal by said disc cam through the intermediary of a cam roller, said slide being guided on a turn table so as to be adjustable and lockable therein in different rotatable positions, and a pin being slidable in a guideway which is provided in an arm which extends laterally from said shaft bearing.

19. A long-arm grinding machine according to claim 18, wherein two of said disc cams are provided which are off set by relative to each other and which are of identical construction and drivably connected to said slide by means of two oppositely 'disposed rollers.

20. A long-arm grinding machine according to claim 16 having a coupling rod one of whose ends is supported on said shaft bearing so as to be pivotable in all directions and the other end of which is supported on a crank circle so as to be pivotable in all directions, and a rotationally driven disc, which forms the crank circle, having a bearing which-in turn is pivotable through an axis extending in parallel to the disc plane and through a joint between the disc and a coupling rod, characterised in that the joint is mounted on a slide which is turned in reciprocable through a cam roller by the driven disc cam, the slide guideway being fixedly joined to the bearing of said disc cam.

Claims

1. A long arm grinding machine for grinding a surface having a grindable width and a grindable length, said machine having an elongated shaft, a grinding head mounted on one end of said shaft, a motor mounted on the other end of the shaft, a machine frame, a tubular shaft bearing mounted on said machine frame and supporting said elongated shaft for pivotable movement over said grindable width, means for permitting the elongated shaft to slide over said grindable length in a direction parallel to a line defined by the longitudinal axis of said elongated shaft when said axis lies parallel to said grindable length and midway of said grindable width, characterised in that there is further provided an eccentric drive for pivoting said shaft bearing, a ratchet mechanism, a pivotably mounted ratchet support supporting said ratchet mechanism, and levers linking said shaft bearing to said ratchet support, said ratchet mechanism including a ratchet wheel and a movable pawl lever having two oppositely constructed pawls which can be changed over into a separate stable position at each end of said grindable length and which entrain said ratchet wheel in the same of two opposite directions until a traverse has been completed in that direction, and a feed mechanism of said machine, said feed mechanism having an immovable element fixedly connected to said machine frame for operative co-operation with said ratchet wheel.

3. A long-arm grinding machine according to claim 1, wheRein said ratchet mechanism has a first tension spring means for retaining said pawl lever in two stable positions, said first tension spring means acting centrally on an end of said pawl lever and being mounted on a position of said ratchet support which is disposed on a line projecting from the center of the end of said pawl lever and the lever pivoting point on said ratchet support, when said pawl lever is in an unstable central position between said two said stable positions.

4. A long-arm grinding machine according to claim 1, wherein said ratchet mechanism further includes a control lever means and an abutment stop lever means which have a common pivoting axis and movable ends distal from said axis, said control lever means acting on the center of said pawl lever to drive said pawl lever into one of said two stable positions, and end stops for indexing said control lever means during movement thereof, said control lever means having a bearing which is independent of the appropriate position of said ratchet support.

6. A long-arm grinding machine according to claim 5, wherein said ratchet support, said control lever means and said stop abutment lever means are journalled on a common shaft which is fixedly joined to said ratchet wheel.

7. A long-arm grinding machine according to claim 4, wherein said control lever means has two abutment surfaces which act on one end of said pawl lever, which abutment surfaces are disposed at a distance therebetween so as to provide said pawls with a limited clearance so that said pawls become detached from the teeth of said ratchet wheel when said ratchet support changes into an opposite direction of movement but without being detached during motion in an appropriate direction.

12. A long-arm grinding machine according to claim 10, wherein said disc is pivotable in a zone between said plane extending parallel with said coupling rod means and a position in whcih the surface described by the motion of said coupling rod means forms a regular circular cone.

13. A long-arm grinding machine according to claim 10, wherein the pivoting axis of said disc bearing extends perpendicularly.

14. A long-arm grinding machine according to claim 10, wherein means are provided for varying the driving speed of said disc which forms said crank circle.

15. A long-arm grinding machine according to claim 10, characterised in that the driving speed of the disc forming the crank circle may be varied.

16. A long-arm grinding machine accoRding to claim 1, wherein said eccentric drive is provided with a disc cam, and said shaft bearing is hingedly joined to a pin which is drivable by said disc cam.

19. A long-arm grinding machine according to claim 18, wherein two of said disc cams are provided which are off set by 180* relative to each other and which are of identical construction and drivably connected to said slide by means of two oppositely disposed rollers.

20. A long-arm grinding machine according to claim 16 having a coupling rod one of whose ends is supported on said shaft bearing so as to be pivotable in all directions and the other end of which is supported on a crank circle so as to be pivotable in all directions, and a rotationally driven disc, which forms the crank circle, having a bearing which in turn is pivotable through an axis extending in parallel to the disc plane and through a joint between the disc and a coupling rod, characterised in that the joint is mounted on a slide which is turned in reciprocable through a cam roller by the driven disc cam, the slide guideway being fixedly joined to the bearing of said disc cam.