WO1987004202A1

WO1987004202A1 - Converting linear movement to rotational movement

Info

Publication number: WO1987004202A1
Application number: PCT/GB1986/000805
Authority: WO
Inventors: Peter David Gill
Original assignee: J.C. Bamford Excavators Limited
Priority date: 1986-01-08
Filing date: 1986-12-30
Publication date: 1987-07-16
Also published as: EP0252110A1; AU6777887A; GB8600391D0; GB2185082A

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

Title: "Converting linear movement to rotational movement"

Description of Invention

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 systems conventionally comprise a pair of hydraulic actuators which are operated such that one actuator pulls a rotational member whilst the 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 will be appreciated that the over centre actuator will oppose continued rotation of the rotatable member.

By ensuring that pistons of the actuators are pivotal ly 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 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 of the actuators, each actuator comprising a piston movable outwardly of a cylinder as fluid is introduced into the cylinder on a first side of the piston, and movable inwardly of the cylinder as fluid is introduced 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 of the second actuator to 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 of the 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 positions and to direct the flow of fluid to the opposite side of the piston of the first or second actuator respectively, during continued movement of the rotatable member to a first or second extreme position.

Thus as one actuator reaches for example an over centre condition, that is a limit position, because the fluid is then directed to the opposite side of the piston of the respective actuator, the actuator does not operate in opposition to the other actuator but rather the actuators will work together so that continued rotation of the rotatable member towards 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 greater torques can be achieved than the maximum torque which 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 of the 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 secondary valve means may then 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 comprises 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 of the rotatable member or the actuators may be sensed to detect when the rotatable member has moved to either of the limit positions. The secondary valve means may be operated directly from the cam follower or through 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 separate valve associated with each actuator, or the secondary 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 vehicle, relative to a frame thereof. Accordingly it is another object of the invention to provide a new or improved excavating vehicle.

According to a second aspect of the invention we provide 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 excavating arm being mounted for rotational movement about a generally vertical axis, and carrying an excavating implement, and the arm being articulated along its length, the rotatable member of the arm being rotated by a system in accordance with the first aspect of the 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 excavating at the extremes of travel of the arm. Hithertofore, this has not always been possible because of insufficient torque being available to move a loaded implement from the extreme positions. The invention will now be described with the aid of the accompanying drawings in which:

FIGURE I is a side diagrammatic view of an excavating vehicle embodying the invention.

FIGURE 2 is an enlarged perspective view of part of the vehicle of Figure I .

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 5 is a view similar to 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 body 1 1 having a ground engaging propulsion means including four wheels 12, a housing 13 for an engine^ and an operator's cab 14.

At the front 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 rear of the vehicle 10, an excavating arm 18 is mounted, the arm comprising a base part 1 9 to which is articulated a dipper arm 20 for movement about a generally horizontal axis 24. At the outer end of the 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 actuator 30 of the pair and a second actuator 31 of the 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 of the valve means 32 is in the (diagrammatic) position shown, i.e. a neutral position, fluid is not directed to either of the 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 the valve 32 to hydraulic line 34. Fluid will pass from hydraulic line 34 through secondary valve means 35,35' which wi ll be described hereinafter, to the actuators 30,31. The actuators 30 and 3 1 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 pivotally 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 valve means 35 via line 41 is fed to the cylinder 37 of actuator 30 on a first annulus side 40 of the piston 36 and will thus cause the piston 36 to move from right to left as seen in figure 3 of the 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' of the second actuator 31 on a second, non annulus side 43 of the piston 36' so as to cause the 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 of the cylinders 37,37' and this fluid will pass back through valves 35,35' and valve 32, to a tank 39 via a further hydraulic line 46. 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 secondary valve means 35,35' so as to feed fluid under pressure via line 41 to the cylinder 37 of actuator 30 on a second non-annuius side 46 of the piston 36, and simultaneously, will feed fluid to the cylinder 37' associated with the second actuator 31 on the first annulus, side 47 of the piston 36' so as to cause the operating element 38' 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 particularly to Figure 4b the connections 50,51 , between the actuators 30 and 1 and the post 26 are shown. In figures 4a and 4b the post 26 is illustrated diagramatically, a typical cross section of the part of the post to which the connections 50, 51 are made being seen in figure 5. It will be appreciated that between limits of travel, the connections 50 and 51 will each be on opposite sides of a generally vertical axis 52 of rotation of the post 26. A typical position is shown in dotted lines in Figure 4b. 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 wil l lie in the same plane as the axis of rotation 52. In a conventional arrangement continued movement of the post 26 in an anti¬ clockwise direction will result in the actuators 30 and 31 working in opposition to one another, so that the actuator 30 will tend to oppose continued movement of the post 26. Because the volume of the chamber at the non annulus side 46 of the piston 36 of the actuator 30 is larger than the volume of the chamber at the annulus side 47 of piston 36' less force will be developed by actuator 30 in an over -centre condition compared to the actuator 31 which is causing the continued anti-clockwise movement of post 26. Thus the post 26 wil l continue to move, although the torque which can be developed beyond the limit position, will be severely limited by the effect of actuator 30. It will be appreciated that if the post 26 is rotated in a clockwise sense as seen in Figure 4b, the same condition 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 invention, 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 diagramatically seen in Figure 3. Now fluid wi ll be fed from line 34 not to the first annulus side 40 of piston 36, but rather the second non-annulus side 46 of the piston 36 so that the actuators 30 and 31 will no longer work 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 of valve 35' wi ll be operated (to the left as seen in figure 3) so that fluid will then be fed from hydraulic line 34 not to first non annulus side 43 of the piston 36', but rather to the second, annulus side 47 of the piston 36', again so that the 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' io the positions shown in figure 3 and are moved against the springs S,S' to change the side of the pistons 36,36' to which fluid is directed.

Thus as the post 26 moves back through 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 embodiment, operated by cams 54 and 55 which are shown in Figure 4a. In this embodiment, the cam 54 acts directly on an operating part 56 of valve 35, when the post 26 moves beyond the limit position at which the actuator 30 reaches its over centre condition, whilst the 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 of the cams 54 and 55 acting directly on the valves 35 and 35' respectively, a suitable linkage could be provided between them. It will be appreciated that in this embodiment, the operating parts 56 and 57 act 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 3 1 respectively. The operating parts 56 and 57 of valves 35,35' bear again, directly, on the cams 60 and 61 so that when the post 26 has rotated beyond a l imit position in which for example actuator 30 reaches an over centre condition, the valve 35 will be actuated to ensure that fluid is directed to the opposite side of the piston 36 to 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 of the post 26 to its limit position.

Again if required, instead of the 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 (or the cams 54 and 55 in the Figure 4a embodiment) acting directly on the valves 35,35' or indirectly 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 a^' single valve block, or any other secondary 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 l inear 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 of the invention may be applied to any other situation in which it is desired to use a pair of linear actuators to rotate a member about an axis. In such other application, 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, or the accompany¬ ing 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 diverse forms thereof.

Claims

CLAIMS:

1. A system for converting linear movement of first (30) and second (31 ) fluid operated actuators into a rotational movement of a rotatable member (26) about an axis (52) transverse to the direction of linear movement of each of the actuators (30,31 ) each actuator comprising a piston (36,36') movable outwardly of a cylinder (37,37') as fluid is introduced into the cylinder (37,370 on a first side (46,43) of the piston (36,36') and movable inwardly of the cylinder (37,37') as fluid is introduced into the cylinder on a second opposite side (40,47) of the piston (36,36') characterised in- that the system includes valve means (35,350 to direct fluid to the first side (46) of the piston (36) of the first actuator (30) and to the second side (47) of the piston (360 of the second actuator (31 ) to move the rotatable member (26) in one direction of rotation about the axis (52) to a first limit position, and to direct fluid to the first side (43) of the piston (36') of the second actuator (31 ) and to the second side (40) of the piston (36) of the first actuator (30) to move the rotatable member (26) in a second opposite direction of rotation about the axis (52) to a second limit position, means (54,55; 60,61 ) to sense when the rotatable member (26) has been rotated in either direction to the first or second limit positions and to direct the flow of fluid to the opposite side of the piston (36,360 of the first or second actuator (30,31 ) respectively, during continued movement of the rotatable member (26) to a first or second extreme position.

2. A system according to Claim I characterised in that the means (54,55) which sense when the rotatable member (26) has been rotated in either direction to the first or second limit positions comprise one or more cams (54,55) carried by the rotatable member (26), which cam or cams (54,55) are each engaged by a cam follower (56,57) of a secondary valve means (35,350 so that when the rotatable member (26) moves to and beyond the limit position, the secondary valve means (35,350 is operated to cause the flow of fluid to be directed to the opposite side of the piston (36,360 of the respective actuator (30,31 ).

3. system according to Claim I characterised in that the sensing means comprises a cam (60,61 ) carried by each of the actuators (30,31 ), which cams have cam followers (56,57) engaged therewith to operate a secondary valve means (35,350 when the rotatable member (26) moves to and beyond the limit position.

4. A system according to Claim 2 or Claim 3 characterised in that the secondary valve means (35,350 is operated directly from the cam follower (56,57).

5. A system according to Claim 2 or Claim 3 characterised in that the secondary valve means (35,350 is operated through a linkage from the cam follower (56,57).

6. A system according to Claim 2 or Claim 3 characterised in that the secondary valve means (35,350 is operated from the cam followers (56,57) via electrical switches which cause electrical means to operate the secondary valve means.

7. A system according to any one of Claims 2 to 6 characterised in that the secondary valve means comprises, a separate valve (35,350 associated with each actuator (30,31 ).

8. A system according to any one of Claims 2 to 6 characterised in that the secondary valve means comprises a combined valve associated with both of the actuators (30,31 ).

9. A system according to any one of the preceding claims when applied to rotate an excavating arm (18) of an excavating vehicle (10) relative to a frame (25) thereof.

10. An excavating vehicle comprising a body (1 1 ), ground-engaging propulsion means (12) to enable the vehicle H O) to move, a frame (25) on the body and carrying a rotatable member (26) of an excavating arm ( 18), the excavating arm (18) being mounted for rotational movement about a generally vertical axis (52) and carrying an excavating implement (21 ), the arm ( 18) being articulated along its length, the rotatable member (26) of the arm ( 18) being rotated by a system in accordance with any one of the preceding claims.