GB2100171A - A power assisted tool - Google Patents

Abstract

The power assisted tool which can be operated with one hand, includes a body (33), two mutually facing work engaging members (22, 32) a handle (27) pivotally mounted on the body (about axis 27B) and operably connected via a link (30) to member (32) so that pivotal movement of the handle in a direction toward the body causes member (32) to move toward member (22), the body housing a gas reservoir (23), a one way valve and a load responsive device. The tool is arranged so that when a reactive load between members (22, 32) exceeds a preset value during a work gripping or cutting operation, the load responsive device responds to said load to open the one- way valve to permit gas to flow from the reservoir and through passage (29B) to assist in the work operation by acting upon a piston (29) carrying the pivot (29A) connecting the link (30) with the handle. <IMAGE>

Description

SPECIFICATION A power assisted tool This invention relates to power assisted tools which are provided with gas operated assistance from a supply of gas such as carbon dioxide or nitrous oxide. Known gas powered tools are used in locations provided with a compressed air reservoir from which the tool is supplied via a flexible pipe connection. Such tools tend to be of heavy construction and their operation is initiated by the user holding the tool in one hand and admitting the compressed air to the tool by opening a valve with the other hand.

It is an aim of the invention to provide a tool, such as pliers, wire cutters or secateurs which is capable of being operated in one hand and which is capable of applying light (non-assisted), and heavy (gas assisted) loads at the operating jaws.

According to the invention, there is provided a power assisted hand tool comprising a body, two mutually facing work engaging members, a handle pivotally mounted on the body and operably connected to said members so that pivotal movement of the handle in a direction toward the body causes relative closing movement of the members toward each other, and wherein the body houses a reservoir containing a gas under pressure, a one way valve and a load responsive device, the tool being arranged so that when a reactive load between the members exceeds a preset value during a work gripping or cutting operation, the load responsive device responds to said load to open said one way valve to permit gas to flow from the reservoir to assist in the work operation.

Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal cross-section through a load reactive device.

Figure 2 is a longitudinal cross-section through a hand tool in the form of a pair of secateurs according to the invention and incorporating the device of Figure 1, and Figure 3 shows a modification of the load reactive device of Figure 1 which employs a refillable gas cartridge.

Referring to Figures 1 and 2, the load responsive device 21 forming part of the gas assisted hand tool T (shown as a pair of garden secateurs), includes a load transmitting member 1 attached by fork connection 1 B to a work engaging anvil 22 of the tool. Member 1 has an integral sensor rod 1 A slidably mounted in a cylinder bore 4A and biassed to the left as viewed in Figure 1 by a compression spring 3 acting between cylinder 4 and an abutment 2 screwthreadedly attached to member 1. An enlarged portion 4B of the cylinder bore is closed by a cylinder head 5 screwthreadedly fixed to the cylinder. Within head 5 is secured a gas supply connector 14 providing a screwed male connector 1 4A for connection to a gas cartridge 23 and providing a gas supply channel 19 which is enlarged at 14B to receive a ball 12 engageable with valve seat 13 to define a one way valve.

Slidably housed within cylinder portion 4B is a piston 17 having a piston rod 17A slidable in bore 4A. Piston 17 is biassed to the left as viewed in Figure 1 by a low rated spring 16, and if, as will be described later, the piston is moved to the right, an integral probe 18 is brought into engagement with ball 12 to lift it off its seat and hence open the one-way valve; movement of the ball 12 is guided by ribs 15 which are integrally formed with connector 14 and which ensure that the ball does not obstruct gas flow. With the one way valve open, gas is permitted to flow from the cartridge 23 via channel 19 and valve seat 13 to outlet passages 10 and 29B, Pressure can be released from the gas space to the right of the piston 1 7 by operation of a vent 6 consisting of sealing ring 7 and ball 8 biassed against ring 7 by spring 9.

The above described device 21 and cartridge 23 are housed in hand tool body 33 which is provided with cylinder bores 33A and 33B in which are positioned pistons 31 and 29 respectively, and provided with bore 33C in which is positioned anvil 22. Cooperating with, and mutually facing, anvil 22 is a work cutting blade 32 extending laterally from piston 31. Mounted on body 33 for pivotal movement about axis 27B is a handle 27 which is secured to an end of piston 29 via connecting screw 28; by means of link member 30 and connecting pins 29A and 31 A, piston 29 is connected for simultaneous movement with piston 31. Thus pivotal movement of handle-27 toward body 33 causes relative closing movement of members 22 and 32.

Assuming that an article to be cut is positioned between members 22 and 32, and that the tool is gripped in one hand so that handle 27 is pivoted relative to the body 33-to bring the members into engagement with the article, then the load now exercised by cutting blade 32 is transmitted, via the article, to anvil 22 which causes sensor rod 1 A to slide within bore 4A to the right as viewed in Figure 1. If during the cutting operation, the load acting on rod 1 A is below a value set by spring 3, the cutting operation can be completed without gas assistance.If, however, the load is of sufficient value to compress spring 3 to allow rod 1 A to engage piston assembly 1 7, 1 7A, 1 8 and moves it to the right, then probe 18 of piston 17 will open the one way valve allowing gas to flow from the cartridge 23 via passages 19, 10 and 29B to the bore 33B where the gas pressure will urge piston 29 to the right thereby applying gas assistance to the movement of cutting blade 32 (via link 30) in its closing or cutting direction.

The diameter of piston 29 should be larger than that of piston 17 to ensure that the thrust exerted by piston 29 and transmitted to cutting blade 32, is greater than the thrust reaction of the anvil 22 occasioned by gas pressure acting on piston 17.

In the example described, piston 29 would be of the order of 35 millimetres in diameter, providing a thrust of about 500 kilograms at normal ambient temperature and gas pressure of about 50 bar), and the diameter of piston 17 would be about 10 millimetres.

Completion of the cutting of the article brings cutting blade 32 into contact with anvil 22, and a vent striker 27A on handle 27 into contact with a vent valve actuating pin 34; further movement of the handle 27 toward body 33 causes pin 34 to unseat ball 8 of vent valve 6 to release to atmosphere the gas acting on pistons 17 and 29.

Relaxation of the grip on the tool allows return spring 35 to pivot the handle away from body 33 and the cutting blade to retreat from anvil 22.

The rate of the spring 3 is chosen so that the load necessary to compress it to a length which permits sensor rod 1 A to piston contact rod 17A, corresponds to the maximum load that can be applied by the operator's hand grip on the handle 27; individual minor adjustments can be effected by varying the axial position of abutment 2 relative to member 1.

To remove and assemble a new gas cartridge 23, retainer 26 is first unscrewed, the old cartridge removed, a new one inserted, and the retainer refitted; the refitting of the retainer causes a narrow neck of the cartridge to enter gas sealing ring 24 and a sealed end of the cartridge to be pierced by a pin (not shown) permitting gas to enter passage 19.

The arrangement of Figures 1 and 2 uses a gas cartridge which is a conventional cartridge currently available for use with soda syphons etc.

In an alternative form of cartridge (see Figure 3), the one way valve 12, 13 of head 5 (Figure 1) is now incorporated as members 42, 43 into the cartridge construction, which is screwthreadedly attached to head 5 via male connector 41 and gas sealed thereto by the compression of washer 40.

With the construction of Figure 3, the piercing pin and retainer 26 are omitted, and the cartridge becomes refillable.

Claims (6)

1. Apower assisted hand tool comprising a body, two mutually facing work engaging members, a handle pivotally mounted on the body and operably connected to said members so that pivotal movement of the handle in a direction toward the body causes relative closing movement of the members toward each other, and wherein the body houses a reservoir containing a gas under pressure, a one way valve and a load responsive device, the tool being arranged so that when a reactive load between the members exceeds a preset value during a work gripping or cutting operation, the load responsive device responds to said load to open said one way valve to permit gas to flow from the reservoir to assist in the work operation.

2. The hand tool of Claim 1, wherein the load responsive device includes a piston and sensor rod both slidably housed in a cylinder and urged apart by a biassing spring, said rod being secured for movement with one of said members, the device being arranged so that an increasing reactive load between said members due to pivotal movement of the handle causes said one member to be moved against its spring bias and, at said preset value of load, is urged into engagement with said piston which is moved to open said one way valve.

3. The hand tool of Claim 2, including a second piston housed in a second cylinder and secured for movement with said handle, the other member being connected to second piston for movement therewith, and said second cylinder being supplied with gas when said one way valve is opened.

4. The hand tool of Claim 3, wherein the diameter of the second piston is larger than that of the first mentioned piston.

5. The hand tool of Claims 2, 3 or 4, including means for varying the biassing force of said spring whereby to adjust said preset value of load.

6. A power assisted hand tool substantially as herein described with reference to Figure 2 when taken in conjunction with Figures 1 or 3 of the accompanying drawings.