GB2185082A - Converting linear movement to rotational movement - Google Patents

Abstract

A system for converting linear movement to a rotational movement such as for causing rotation of an excavating arm (18) of an excavating vehicle (10) relative to a frame (25) about an axis (52) transverse to the direction of linear movement of each of a pair of double acting actuators (30, 31), comprises valve means (35, 35') to reverse the flow of fluid to one of the actuators as the actuator reaches an over-centre condition.

Description

SPECIFICATION Converting linear movement to rotational movement This invention relates to a system for converting linear movement to a rotational movement.

More particularly, but not exclusively, the invention relates to such a system for causing rotation of an excavating arm of an excavating vehicle relative to a frame using a pair of linear actuators. Such sys tems conventionally comprise a pair of hydraulic actuators which are operated such that one actuator pulls a rotational memberwhilstthe other actuator pushes the rotational member about a rotational axis.

However, at the extremes of rotation where a large amount of rotation has taken place, it is common for one of the actuators to be in an over centre condition.

The actuators continue to operate as before but it be appreciatedthatthe over centre actuators will oppose continued rotation of the rotatable member.

By ensuring that pistons ofthe actuators are pivotally secured to the rotatable member, continued rotation even when one actuator is over centre can be ensured as less torque will be developed by the over centre actuator because of the geometry of the actuators.

However, the torque which can be achieved in known systems, at least at or near the extremes of rotation, is severely limited by the opposition of the over centre actuator.

Accordingly it is an object of the present invention to provide a new or improved system for converting linear movement to rotational movement.

According to one aspect of the invention we provide a system for converting linear movementoffirst and second fluid operated actuators into a rotational movement of a rotatable member about an axis transverseto the direction of linear movement of each of the actuators, each actuator comprising a piston movable outwardly of a cylinder as fluid is in troduced into the cylinder on a first side ofthe piston, and movable inwardly of the cylinder asfluid is intro duced into the cylinder on a second opposite side of the piston, the system including valve means to direct fluid to the first side ofthe piston ofthe first actuator and to the second side ofthe piston ofthe second actuatorto move the rotatable member in one direction of rotation about the axis to a first limit position, and to direct fluid to the first side ofthe piston of the second actuator and to the second side ofthe piston of the first actuator to move the rotat able member in a second qpposite direction of rota tion about the axis to a second limit position, means to sense when the rotatable member has been rota ted in either direction to the firstorsecond limit posi tions and to direct the flow offluid to the opposite side of the piston of the first or second actuator re spectively, during continued movement ofthe rotat able memberto a first or second extreme position.

Thus as one actuator reaches for example an over centre position, that is a limit position, because the fluid isthen directed to the opposite side ofthe piston of the respective actuator, the actuator does not operate in opposition to the other actuator but rather the actuators will worktogetherso that continued rotation ofthe rotatable membertowards its first or second extreme position is not opposed.

It has been found that in a system in accordance with the invention, the torque which can be achieved at the first and second extreme positions is considerably improved compared with conventional arrangements, and even greatertorques can be achieved than the maximumtorquewhich can be achieved in rotating the rotatable member between its first and second limit positions.

By "over centre condition" we mean a position beyond that in which the direction of operation of the actuator and the axis of rotation ofthe rotatable member lie in a common plane.

In one embodiment, the means which sense when the rotatable member has been rotated in either direction to the first or second limit positions may comprise one or more cams carried by the rotatable member, which cam or cams may each be engaged by a cam follower of a secondary valve means so that when the rotatable member moves to and beyond the limit position, the secondary valve means is operated, which secondaryvalve means maythen cause the flow of fluid to be directed to the opposite side of the piston of the respective actuator.

In another embodiment, the sensing means cam prises a cam carried by each of the actuators, which cams may have cam followers engaged therewith to operate a secondary valve means when the rotatable member moves to and beyond the limit position. It will be appreciated that as the rotatable member rotates, the actuators will themselves move so that either the movement ofthe rotatable member or the actuators may be sensed to detect when the rotatable member has moved to either ofthe limit posi- tions.

The secondary valve means may be operated directlyfrom the cam followerorthrough a linkage, or the cam follower may operate electrical switches which may cause solenoids for example, or other electrical means, to operate the secondary valve means.

The secondary valve means may comprise a sep arate valve associated with each actuator, or the sec ondary valve means may comprise a combined valve associated with both of the actuators.

The invention is particularly applicable to a system for rotating an excavating arm of an excavating veh icle, relative to a frame thereof.

Accordingly it is another object of the invention to provide a neworimproved excavating vehicle.

According to a second aspect ofthe invention we provide an excavating vehicle comprising a body, ground engaging propulsion means to enablethe vehicleto move, a frame on the body and carrying a rotatable member of an excavating arm, the excavat ing arm being mounted for rotational movement about a generally vertical axis, and carrying an ex cavating implement, and the arm being articulated along its length,the rotatable memberofthearm being rotated by a system in accqrdance with the first aspect ofthe invention.

Because maximum torque can be achieved at the extremes of rotation, an operator of such an excavating vehicle can thus use the implement for excavat- ing at the extremes oftravel ofthe arm. Hithertofore, this has not always been possible because of in sufficienttorque being availableto move a loaded implementfrom the extreme positions.

The invention will now be described with the aid of the accompanying drawings in which: Figure lisa side diagrammatic view of an excavating vehicle embodying the invention.

Figure2 is an enlarged perspective view of part of the vehicle of Figure 1.

Figure 3 is a diagrammatic illustration of a system in accordance with the invention.

Figures 4a and 4b are plan diagrammatic views of parts of the system not shown in Figure 3, and Figure 5is a vfew similarto the combined views of Figures 4a and 4b which shows an alternative embodiment.

Referring first to Figures 1 and 2, an excavating vehicle 10 comprises a body11 having aground engaging propulsion means including fourwheels 12, a housing 13foran engine, and an operator's cab 14.

Atthefront of the vehicle, a loading arm 15 is provided which carries at the outer end thereof, a loading implement 16 such as a bucket.

At the rearofthevehicle 10, an excavating arm 18 is mounted, the arm comprising a base part 1 9to which is articulated a dipper arm 20 for movement about a generally horizontal axis 24. Atthe outer end ofthe dipper arm 20, an excavating implement 21 is provided which again comprises a bucket.

The dipper arm 20 is movable relative to the base 19 by means of a hydraulic actuator 22, and the excavating implement 21 is movable relative to the dipper arm 20 due to a further hydraulic actuator 23.

The excavating arm 18 is carried on a frame 25 which is movable laterally of the vehicle 10, and is mounted via a rotatable member comprising a post 26 which is rotatable relative to the frame 25 by means of a pair of hydraulic actuators 30 and 31 which are best seen in Figure 2.

Referring now also to Figure 3, a first actuator30 of the pair and a second actuator31 ofthe pair, are each connected via hydraulic lines 27/41,34/45, or 27'/42, 34/45, to a valve means 32 which receives fluid under pressure from a pump 33. When an operating member ofthe valve means 32 is in the (diagrammatic) position shown, i.e. a neutral position, fluid is not directed to either ofthe actuators 30 and 31. However, if the operating member of the valve means 32 is moved to the right as seen in the drawings, fluid may pass through thevalve 32to hydraulicline34. Fluid will passfrom hydraulicline 34 through secondary valve means 35,35' which will be described hereinafter, to the actuators 30,31.The actuators 30 and 31 each comprise a piston 36,36' respectively, movable within a cylinder 37,37', the pistons 36,36' being connected to an operating element 38,38' which is pivotal ly secured to a crank part 39 which is rigidly secured to the post 26, via connections 50. Fluid which passes from line 34 through the secondary valye means 35 via line 41 is fed to the cylinder 37 of actuator 30 on a first annulus side 40 ofthe piston 36 and will thus cause the piston 36to move from right to left as seen in Figure 3 ofthe drawings so that the operating element 38 will be withdrawn into the cylinder 37.Conversely, fluid which passes from line 34 through secondary valve means 35', passes via a hydraulic line 42 to the cylinder 37' ofthe second actuator 31 on a second, non annulus side of the piston 36' so as to causethe piston 36' to move from right to left as seen in Figure 3 of the drawings, so that the operating element 38' is extended from the cylinder 37'.

This will cause the post 26 of the excavating arm 18 to rotate in a clockwise direction as seen in Figure 2.

As fluid is introduced into the cylinders 37,37' as described, fluid will be expelled from the opposite sides ofthe cylinders 37,37' and this fluid will pass backthrough valves 35,35' and valve 32,to a tank 39 viaafurtherhydraulicline46.

Conversely, if the operating member of the valve means 32 is moved to the left as seen in the drawings, hydraulic fluid will be passed to hydraulic line 45 and will pass through each of secondaryvalve means 35,35' so as to feed fluid under pressure via line 41 to the cylinder 37 of actuator 30 on a second non-annulus side 46 of the piston 36, and simu Itaneously, will feed fluid to the cylinder37' associated with the second actuator 31 on the first annulus, side 47 ofthe piston 36' so as to cause the operating element38' to be withdrawn into the cylinder 37'.

This will result in anti-clockwise movement of the post 26 relative to the frame 25 as seen in Figure 2 because the post receives a bearing pin around which the post 26 may rotate.

Referring particularlyto Figure b the connections 50,51, between the actuators 30 arid 31 and the post 26 are shown. In Figures 4a and 4t)the post 26 is illustrated diagramatically, a typical crpss section ofthe post being seen in Figure 5. Itwill be appreciated that between limits of travel, the connections 50 and 51 will each be on oppositesidesofagenerallyvertical axis 52 of rotation ofthe post 26. Atypical position is shown in dotted lines in Figure 46. However, as the post 26 swings anti-clockwise for example, eventually the post will reach a limit position when the actuator 30 will be in an over centre condition which is shown in full lines, in which the direction of operation of the actuator 30 will lie in the same plane as the axis of rotation 52.In a conventional arrangement continued movement ofthe post 26 in an anticlockwise direction will result in the actuators 30 and 31 working in opposition to one another, so thatthe actuator 30 will tend to oppose continued movement ofthe post 26.

Because the volume of the chamber at the non annulus side 46 of the piston 36 of the actuator 30 is largerthan the volume of the chamber at the annulus side 47 of piston 36' less force will be developed by actuator30 compared to the actuator 31 which is causing the continued anti-clockwise movement of post 26. Thus the post 26 will continue to move, although the torque which can be developed beyond the position, will be severely limited by the effectof actuator 30.

It will be appreciated that if the post 26 is rotated in a clockwise sense as seen in Figure 4b, the same con dition would occur when the actuator 31 in an over centre condition with the actuator 31 oppositing further clockwise movement.

In the system in accordance with the present in- vention, this problem is overcome by providing the secondary valve means 35 and 35'. As the post 26 is rotated to the limit position when for example, actuator 30 is in an over centre condition, the secondary valve 35 will be operated by moving an operating member of the valve 35 to the left as diagrammatically seen in Figure 3. Nowfluidwill be fed from line 34 nottothefirstannulus side 40 of piston 36, but ratherthe second non-annulus side 46 of the piston 36 so that the actuators 30 and 31 will no longerwork in opposition but will work together.

Conversely, when post 26 is moved in a clockwise sense until actuator 31 is an over centre position, an operating member ofvalve 35' will be operated (to the left as seen in Figure 3) so that fluid will then be fed from hydraulic line 34 nottofirst non annulus side 43 of the piston 36', but rather two the second, annulus side 47 ofthe piston 36', again sothatthe actuators 30 and 31 will work together and not in opposition limiting the torque developed beyond the over centre condition.

Preferably, the valves 35,35' are biased by springs S,S' to the positions shown in Figure 3 and are moved against the spring S,S' to change the side of the pistons 36,36'to which fluid is directed.

Thus asthe post26 moves backthrough the limit positions, the springs S,S' will return the valve means 35,35' to the position shown.

The secondary valve means 35 and 35' are one em bodiment,operated bycams54and55whichare shown in Figure 4a. In this embodiment, the cam 54 acts directly on an operating part56 of valve35, when the post 26 moves beyond the limit position at which the actuator 30 reaches its over centre condi tion, whilstthe cam 55 acts directly on an operating part 57 of the valve 35' when the post 26 is rotated in a clockwise sense beyond a limit position in which the actuator 31 reaches an over centre condition. If desired, instead ofthe cams 54 and 55 acting directly on the valves 35 and 35' respectively, a suitable lin kate could be provided between them.

It will be appreciated that in this embodiment, the operating parts 56 and 57 acts as cam followers.

Referring now to Figure 5, an alternative arrangement is shown. Instead of cams 54,55, being carried by the rotatable member i.e. post 26, cams 60 and 61 are carried on the hydraulic actuators 30 and 31 respectively. The operating parts 56 and 57 ofvalves 35,35' bear again, directly, on the cams 60 and 61 so that when the post 26 has rotated beyond a limit position in which forexample actuator30 reaches an over centre condition, the valve 35 will be actuated to ensure that fluid is directed to the opposite side of the piston 36to that which the fluid has been directed during rotation of the post 26 to its limit position.

Conversely, when the post 26 rotates clockwise beyond its limit position so that the actuator 31 reaches an over centre condition, the cam 61 will act on the operating part 57 to operate valve 35' so that fluid is fed to the opposite side of the piston 36' of actuator 31 to that which the fluid has been directed during rotation ofthe post 26 to its limit position.

Again if required, instead ofthe cams 60 and 61 acting directly on the operating parts 56 and 57 of valves 35,35' which act as cam followers, suitable linkages could be provided between the valves 35,35' and the cams 60,61.

In another arrangement, instead of the cams 60 and 61 (orthe cams 54 and 55 in the Figure 4a embodiment) acting directly on the valves 35,35' or indi rectly through linkages, the cams may operate solenoid or other electrically operated switches which in turn, operate the valves 35 and 35'.

Various modifications may be made without departing from the scope of the invention. In particular, instead of providing a pair of separate secondary valves 35 and 35', the valves could be contained within asinglevalveblock,oranyothersecondary valve means could be provided to feed fluid to an opposite side of an actuator piston as the rotatable member 26 moves beyond its limit position(s).

Although the invention has been described in relation to converting the linear movement of a pair of hydraulic actuators into a rotational movement of an excavating arm 18 of an excavating vehicle, about a generally vertical rotational axis, the system ofthe invention may be applied to any other situation in which it is desired to use a pair of linear actuators to rotate a memberaboutan axis. In such otherapplication, instead of a hydraulic system, a pneumatic arrangement may be provided.

It will be appreciated that the valves 35,35' and 32 as shown in the drawings are considerably simplified compared with a practical arrangement.

The features disclosed in the foregoing description, orthe accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverseformsthereof.

Claims (12)

1. A system for converting linear movement of first and second fluid operated actuators into a rotational movement of a rotatable member about an axis transverse to the direction of linear movement of each ofthe actuators, each actuator comprising a piston movable outwardly of a cylinder as fluid is in troduced into the cylinder on a first side of the piston, and movable inwardly of the cylinder asfluid is intro- duced into the cylinder on a second opposite side of the piston, the system including valve means to direct fluid to the first side of the piston of the first actuator and to the second side of the piston ofthe second actuatorto movethe rotatablememberin one direction of rotation about the axis to a first limit position, and to direct fluid to the first side ofthe piston of the second actuator and to the second side of the piston of the first actuator to move the rotatable member in a second opposite direction of rotation about the axis to a second limit position, means to sense when the rotatable member has been rotated in either direction to the first or second limit posi tions and to directthe flow of fluid to the opposite side of the piston ofthefirstorsecond actuatorre spectively, during continued movement of the rotatable member to a first or second extreme position.

2. A system according to Claim 1 wherein the means which sense when the rotatable member has been rotated in either direction to the first or second limit positions may comprise one or more cams carried by the rotatable member, which cam or cams may each be engaged by a cam follower of a sec- ondaryvalve means so that when the rotatable member moves to and beyond the limit position,the secondary valve means is operated to cause the flow offluid to be directed to the opposite side ofthe piston of the respective actuator.

3. A system according to Claim 1 whereinthe sensing means comprises a cam carried by each of the actuators, which cams may have cam followers engagedtherewithto operate asecondaryvalve means when the rotatable member moves to and beyond the limit position.

4. A system according to Claim 2 or Claim 3 wherein the secondary valve means is operated directlyfrom the cam follower.

5. A system according to Claim 2 or Claim 3 wherein the secondary valve means is operated through a linkage.

6. A system according to Claim 2 or Claim 3 wherein the cam follower operates electrical switches which cause electrical means to operate the secondary valve means.

7. Asystem accordingto anyoneofClaims2to6 wherein the secondary valve means comprises a separate valve associated with each actuator.

8. A system according to any one of Claims 2 to 6 wherein the secondary valve means comprises a combined valve associated with both ofthe actuators.

9. A system according to any one of the preceding claims when applied for rotating an excavating arm of an excavating vehicle, relative to a frame thereof.

10. A system substantially as hereinbefore des cribed with reference to and as shown in the accompanying drawings.

11. An excavating vehicle comprising a body, ground engaging propulsion means to enable the vehicle to move, a frame on the body and carrying a rotatable member of an excavating arm, the excavat ing arm being mounted for rotational movement about a generallyvertical axis, and carrying an ex cavating implement, and the arm being articulated along its length, the rotatable member of the arm being rotated buy a system in accordance with any one of Claims 1 to 10.

12. An excavating vehicle substantially as here inbefore described with reference to and as shown in the accompanying drawings.