This invention relates to a semi -rotary f luid actuator , which term as used here in means a f luid operated actuator capable of translating a manually powered mechanical control into fluid powered semi-rotary motion ( i.e. rotation through less than a full circle).

An example of a device in which the actuator may be incorpo¬ rated is an hydrau lic shear ing tool , e.g. sc is sors , tin snips or bolt cutters. In such a device, the actuator serves to translate a manual control applied to the handle into an hydraulically powered slave motion of the shearing blades. Other examples of application of the actuator are the control of butterf ly valves by a small Bowden-type cable and cable control of door actuation.

In a conventional non-powered shearing tool, shearing forces of such high magn i tude can be requ ired that the neces sary mechanical advantage has to be obtained by the provision of long handles , thus making the tool unwieldy, tiring to operate and difficult to control. The present invention aims to provide a semi -rotary fluid actuator to overcome such di sadvantages .

I n accordance wi th one aspect of the invention, there is provided a semi-rotary fluid actuator comprising a housing, a bushing rotatab le relative to the hous ing , at least one variable volume arcuate chamber defined between the bushing and the hous ing and valve means rotatab le relative to the

bushing for controlling the flow of fluid to and from the chamber(s) in- dependence upon the relative angular position of the bushing and the valve means in such a manner that upon movement of the valve means from a neutral position a torque is applied to the bushing to cause the bushing to follow the movement of the valve means.

In use, the housing and the bushing are connected to the relatively movable parts of a pivot and the valve means are movable by means of a manual control member.

In a preferred embodiment of the invention, the bushing has a vane which partitions an hydraulic chamber formed between the bushing and the housing, and the bushing has ports through which hydraulic fluid can flow to and from the chambers under the control of the valve means to develop a differential hydraulic driving torque on the vane which thus rotates the bushing.

Conveniently, the valve means may comprise a spool posi¬ tioned within the bushing and cooperating with the ports in the bushing to regulate the supply of fluid in dependence upon the angular of the spool within the bushing.

In accordance a second aspect of the present invention, there is provided a shearing tool having a reference handle, a reference blade rigidly connected to the reference handle, a control handle and a slave blade mounted at a common pivot assembly to the junction of the reference handle and refe¬ rence blade, and a hydromechanical semi-rotary actuator

incorporated in said pivot assembly, said actuator compri¬ sing a housing to which the reference handle and blade are rigidly connected, a bushing rotatable within the housing and to which the slave blade is rigidly connected, the bushing having a vane which partitions an arcuate hydraulic chamber formed between the housing and said bushing, and a spool rotatable within the bushing and to which the control handle is rigidly connected, said spool having supply and return cavities for hydraulic fluid which by manual opera¬ tion of the handles are placed in communication with the arcuate chamber through ports in the bushing, thereby to develop a differential driving torque on the vane which causes the blades to perform a powered shearing action.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 shows a shearing tool in side elevation;

Figure 2 is a partly cross-sectioned plan view of the operating head of the tool; and

Figure 3 is an axial cross-section through the pivot assembly of the tool.

The shearing tool shown in the drawings has a pair of handles and a pair of shearing blades. The handles comprise a reference handle 10 and a control handle 12, and the blades comprise a reference blade 14 and a driven blade 16. The reference handle 10 and reference blade 14 are integral¬ ly interconnected in the region of a pivot assembly 18 by

P

eans of a section 20. The control handle 12 and the driven b lade 16 can turn about the axis of the pivot assembly 18. The pivot assembly 18 incorporates a hydromechanical semi- rotary actuator 22 ( see Figure 1) of the invention.

The actuator 22 comprises a circular housing 24 rigid with the reference handle and reference blade assembly 10 , 14 , 20. Rotatab le in the hous ing 24 is a vaned bushing 26 , to which the driven blade 16 is rigidly connected. An arcuate chamber 28 is defined between the bushing 26 and the housing 24 , and has a radial vane 30 which sub-divides the chamber 28. The bushing 26 bears against the interior of the housing 24 at the ou ter end of said vane, and also at an inward rib 32 on the hous ing which separates the ends of the arcuate chamber 28. S eals , designated 34 and 36 , respectively, are provided at each bearing region.

Within the vaned bushing 26, a spool 38 is rotatable against the inner surface of the bushing 26. The control handle 12 is r igidly connected to the spool 38. The spool 38 is an element wi th four broad, equi-angularly spaced, axial grooves in its surface, diametrically opposite grooves being interconnected by cross bores. The pairs of interconnected grooves constitute cavities which are referenced 40 and 42. Hydraulic fluid is supplied to the cavity 40 through a port 44 and hydraulic fluid can exit from the cavity 42 through a port 46. The ports 44, 46 communicate with hydraulic fluid supply and return lines 48, 50 through passages 52 , 54 bored in the control handle 12.

It will be clear that, in use, when the handles 10, 12 are operated, e.g. by squeezing the control handle 12 towards y*£ the reference handle 10, the spool 38 is rotated within the

V bushing 26.

To the sides of the vane 30 which partitions the hydraulic chamber 28 , the bushing 26 has through ports 56 , 58. When the spool 38 is rotated, the hydraulic f luid supply and return cavi ties 40 , 42 communicate through the respective ports 56 , 58 in the bushing with the hydraulic chamber 28, on respective opposite sides of the vane 30. A differential driving torque is thereby developed across the vane 30 , causing the bushing 26 to rotate. The driven blade 16 is thereby rotated relative to the reference blade 14. This motion continues until the bushing ports 56 , 58 are closed due to said rotation of the bushing 26. More generally, therefore, the driven blade 16 constitutes a slave which is hydraulically driven in response to a manually operated master constituted by the control blade 12.

The invention thus provides an arrangement of shearing tool in which the shearing blades are fluid powered whilst manual positional control is retained by the handles. Manual effort « is not required to provide the full force necessary to

•^ effect the shearing action, and the user can therefore concentrate on control. Clearly, elongated handles to gene¬ rate a substantial mechanical advantage are no longer required, ^* and the bulk, weight and unwieldyness of the tool can thereby be minimi sed. Furthermore, rapid or prolonged

operation of the tool can be achieved without fatigue.

Although particularly described and illustrated in relation to a shearing tool, the invention has general applicability to situations where a powered semi-rotary action of a driven member is required in response to manual control. The actua¬ tor is incorported in the pivot assembly for the driven member and movement of the valve means constituted by the spool may be achieved by any convenient control element, such as a Bowden type cable.

Various modifications of the above-described arrangement are possible within the scope of the invention as set forth in the claims, especially in relation to the manner in which the hydraulic chamber is formed to apply a rotational torque to the bushing.