Fastener driver tools

Abstract

The tool includes an operating piston reciprocable within a working cylinder under the control of a control piston which is normally biased into engagement with a fixed obturating surface. The control piston grips the operating piston and only releases its grip when, after actuation of a trigger, the control piston has moved into a position in which it closes an air exhaust duct.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to compressed-air-operated tools for the driving-in of nails, wire staples or the like, of the kind in which a fixed casing-associated sleeve which carries the working cylinder -- with the operating piston that slides in the latter -- and a control piston is surrounded by a compressed-air reservoir permanently connected to the compressed-air supply line, the inner space of the working cylinder being blocked off relative to the reservoir when the tool is at rest by the control piston which is coaxial with the working cylinder for as long as the latter, when its upper surface is acted upon by compressed air, is pressed against an annular obturating surface of the casing-associated sleeve, and is lifted off the casing-associated sleeve when the upper side of the control piston is relieved of pressure by actuation of the trigger valve.

2. Description of the Prior Art

Such tools are already known and the main design emphasis has been upon the development of control procedures by means of which it is possible to achieve optimum impact efficiency. To achieve this aim, it is important to convert the working capacity of the compressed air with a high degree of efficiency into kinetic energy, i.e., into movement of the operating piston. The energy inherent in the operating piston is then employed by way of an impact-applying rod for driving in the fastener means such as staples, nails and the like. There are three essential factors which must be taken into account if optimum utilisation of the energy is to be achieved. These factors are as follows:

1. The avoidance of too great a fall in pressure during the impact stroke. In order to prevent a fall in pressure, an adequate volume of compressed air must be available within the casing. The aim should be to have the volume in the compressed-air reservoir many times the piston-stroke volume.

2. Valve operation, i.e., the opening and closing of the working cylinder, considerably affects the impact force of the tool (and may even be the most important factor). One should allow the compressed air to expand from the casing into the working cylinder without any loss of pressure. For this, short valve movements and very large cross-sections, as well as maximum speeds of opening for the valve, are required. Further, to avoid a further fall in pressure, the valve should function without any overlap effect, i.e., the inlet and outlet valves must not be open at the same time.

3. During the impact stroke some air pressure may build up beneath the operating piston, thus affecting the impact stroke. This build-up of pressure must be kept as small as possible.

The provision of a large supply of compressed air within the casing is already known from German Pat. Specification No. 1,144,660. In the compressed-air-operated nail-driving tool according to this German specification, the upper part of the working cylinder is free-standing and is surrounded by a compressed-air reservoir. When at rest, the cylinder is blocked off at its upper end by a control piston. In this way, given a maximum size of cross-section for the inlet, only a short lifting movement of the control piston is required. However, the operation of the control piston is poor, since optimum opening speeds cannot be achieved. In addition, no compensatory facility is provided for the air displaced beneath the operating piston.

U.S. Pat. Spec. No. 2,983,922 illustrates a tool in which the volume of air displaced by the operating piston can escape to a compensatory tank. A further tool for driving nails by compressed air is known from German Offenlegungsschrift No. 1,907,069. Here, however, a really expensive valve control system is employed, by means of which the cylinder space beneath the piston can be cleared of air. Control arrangements of such expensiveness, however, make the tool heavy and cause it to work sluggishly.

In addition, U.S. Pat. Spec. No. 2,944,522 illustrates a tool for driving nails by compressed air in which the working cylinder itself performs a valve function, it being axially displaceable. Because of the great mass of the working cylinder, this tool too, however, operates relatively sluggishly. The same thing should also be noted in the tool of German Pat. Spec. No. 1,285,959. In this tool the further point arises that the functions of the inlet and of the outlet are not strictly separated and this affects the actual impact function.

It is an object of the invention to provide a compressed-air-operated tool for driving in nails, wire staples or the like which provides for rapid movements of the control piston and consequently eliminates any overlapping of the inlet and outlet functions.

SUMMARY OF THE INVENTION

The invention consists in an arrangement in which, when the tool is at rest, the control piston grips the operating piston and only releases said grip when, following actuation of the trigger valve and initiation of movement of the control piston, the air-exhaust duct has been closed.

When the control piston first grips the operating piston, the operating piston initially follows the control piston in the latter's lifting movements, until the air-exhaust duct has been closed. Immediately distinct pressure ratios are created in the control piston because of the closure of the air-exhaust duct, the pressure required for releasing the operating piston builds up and the operating piston is released as soon as the air pressure in the control piston exceeds the grip exerted on the operating piston. Immediately the operating piston is released, the compressed air from the reservoir expands into the operating cylinder and the operating piston carries out its impact stroke.

According to a further feature of the invention, the control piston has an axial bore and, as it lifts, it comes against a sealing system which closes the bore. This design is simple and reliable in operation. The control piston is preferably provided with a resilient sealing member which has an annular squeezing lip within which the upper edge of the operating piston is held. The squeezing lip may also be surrounded by a sealing lip which, when the tool is at rest, closes off the working cylinder with respect to the compressed-air reservoir. Consequently, by the use of a single sealing member both the gripping of the operating piston and also the sealing off of the working cylinder from the compressed-air reservoir are effected. Assembly of the tool is facilitated by forming the control piston, a differential member guiding the control piston within a sleeve, and the sealing member as a single functional unit.

The build-up of air pressure in the control piston to effect release of the operating piston from the same is provided for in that, running from a groove in the operating piston equipped with an O-ring, there is provided at least one perforation leading to a transverse channel in the upper surface of the operating piston.

A further feature of the invention is a small annular enlargement at the upper end of the working cylinder into which, upon completion of the return movement of the piston, the sealing ring of the operating piston gets pressed by the compressed air urging the piston upwardly. Through the same compressed air, the sealing ring also gets displaced into its upper position in the groove of the operating piston, with the result that a channel is created through which the compressed air beneath the piston can flow so as to escape through the channels of the operating piston and control piston to the atmosphere.

An annular differential chamber on the control piston may be situated between the upper and lower control ring of the differential member. This differential chamber, which is kept as small as possible, is connected by means of at least one bore to the control chamber situated above the control piston and is sealed off from the control chamber by means of a resilient seal which prevents the passage of air flowing from the control chamber to the differential chamber. Compressed air which infiltrates through any defective sealing members is led away through the bore to the control chamber if the latter is at atmospheric pressure for the triggering of the impact blow. The provision of a differential chamber therefore ensures that the control piston, along with its resilient sealing ring situated between the working cylinder and the compressed-air reservoir, cannot be displaced from its lower closing position by the effects of external shocks, even if atmospheric pressure prevails in the reservoir and control chamber, because a reduction of pressure occurs in the differential chamber upon movement of the control piston and this pressure reduction immediately draws the control piston back to its initial position. Thus, when the nail-driving tool is connected to the compressed-air supply line, any unintentional initiation of an impact blow is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a compressed-air-operated tool for the driving in of wire staples, nails or the like, the tool being shown in its position of rest,

FIG. 2 is a longitudinal sectional view taken through the head of the tool of FIG. 1, with the control piston raised and with the operating piston under control,

FIG. 3 is a longitudinal sectional view through the tool of FIGS. 1 and 2, after the downward travel of the operating piston has been completed, and

FIG. 4 shows the tool according to the invention, with the operating piston executing a return-movement.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The compressed-air-operated nail-driving tool shown in FIG. 1 consists basically of three main components, namely a casing 1, a pistol-grip 2 and a magazine 3. The inner space of the pistol-grip 2 constitutes a compressed-air reservoir for receiving compressed air and holding it ready for operation. In the casing 1 there is a working cylinder 5 which at its axial ends has collar-like reinforcements 6a and 6b. These reinforcements constitute radial guide means of the working cylinder 5 and receive O-rings 7.

The upper half of the working cylinder 5 is coaxially surrounded by a sleeve 8 which is firmly screwed to the casing 1 by means of a thread 9. The working cylinder 5 is secured at its two ends against axial displacement by means of a collar 10 on the sleeve 8 and an end-surface 11 of a flange 12. The flange 12 is rigidly fixed to the casing 1 by means of screws (not shown here). The collar 14 of a retarder ring 15 is gripped between the end-surface 11 of the flange 12 and the end-surface 13 of the working cylinder 5. The retarder ring 15 is thus fixed in its position, as shown in FIG. 1. As a result of the coaxial positioning of the sleeve 8 and the working cylinder 5, there is formed between them a space 16 which constitutes an enlargement and extension of a space 16a. The two spaces 16 receive compressed air for effecting return movement of the operating piston. Bores 17 are provided in the working cylinder for the passage of compressed air into the spaces 16 and 16a. Bores 18 serve to vent the air.

The upper area of the sleeve 8 serves for the reception and guidance of a control piston 19 as well as for the formation of a pressure differential means. Around the periphery of the sleeve 8, large apertures 20 are located through which compressed air can enter from the pistol-grip chamber 4 into the inner chamber of the working cylinder 5 without loss of pressure. The control piston 19 is a differential piston which, with a view to easier assembly, is composed of an interengaging arrangement of a supporting member 21 with a protrusion 22, a differential member 23 and a seal 24. The seal may, for example, consist of the commercial plastics material sold under the Trade Name Vulkollan. A circlip 25 keeps the parts of the control piston firmly together and the mass of the control piston is kept as small as possible so as to achieve maximum switching speed.

Supporting member 21 is provided with a venting bore 26 which extends through the protrusion 22. The control piston 19 carries O-ring seals 27 which seal off the two compressed-air chambers from each other. On the other hand, an O-ring 28 arranged in a groove 28a possesses a control function and ensures that, at the most, only atmospheric pressure prevails in a differential chamber 29. The differential chamber 29 is linked to a control chamber 34 via at least one bore 29a which can be closed by means of the sealing ring 28.

The seal 24 of the control piston 19 is provided at its end face 30 with an outer sealing lip 31 which exercises a sealing function in conjunction with the end surface of the sleeve 8; on the other hand, an inner lip 32 has a squeezing function, and in a manner to be described hereinafter it grips the upper edge of the operating piston 39. The casing 1 is closed off at its upper end by a lid 33 thus forming the control chamber 34. Axially above the protrusion 22 of the supporting member 21 there is a seal 35 inside the lid 33; the distance between the end-surfaces of the parts 22 and 35 defines the length of the stroke of the control piston 19. A cap 36 serves to collect the exhaust air emerging from the bores 37 in the lid 33 and to guide the exhaust air to atmosphere through an opening 38.

To achieve a high speed, the operating piston 39 possesses a mass which is as small as possible. It has a collar 40 to receive an O-ring 41 in a groove 41a and to act as a guide inside the working cylinder 5. When the piston 39 is in its upper terminal position, the O-ring 41 can enter an annular extension 41a (see FIG. 2) of the internal diameter of the working cylinder 5. Adjoining the collar 40 is a neck portion 42 which receives an impact-applying rod 43. The connection between the neck portion 42 and the impact-applying rod 43 is provided by two clamping sleeves 44. The collar 40 is provided with a downwardly-extending peripheral annular flange 45. This flange 45 prevents the veering aside of the retarder ring 15 when there is a powerful impact effect if, for instance, the tool has been fired into the air and the energy is not absorbed by the nail-driving procedure but is all transmitted to the retarder ring. A channel 46 is formed in the upper end surface of the operating piston 39 and this channel communicates, by way of bores 47, with the annular groove 41a of the O-ring 41.

Within the flange 12 is located guide means 49 for the impact-applying rod 43, the guide means possibly consisting of a plastics material, for example the urethane material sold under the Trade Name Vulkollan by Bayer Company consisting of ethylene glycol-adipic acid-polyester in combination with naphthalene-1.5-diisocyanate. The guide means 49 for the impact-applying rod 43 also seals off the inner chamber 50 of the working cylinder 5. The parts 51 of the guiding track 52 for the wire staples and the magazine 3 for receiving the staples are rigidly connected to the flange 12. Interposed ahead of the control piston 19 there is a servo-valve which consists of a valve rod 53 and of a sleeve 54, it being possible to actuate these with the aid of a trigger 55.

FIGS. 1 to 4 show the tool in several operating positions. FIG. 1 shows the arrangement of the parts when the tool is at rest. The valve rod 53 is retained in its lowermost position by compressed air acting against its collar 56. An O-ring 57 on the rod is positioned so that it does not prevent flow of compressed air from the pistol-grip chamber 4 which passes by way of a bore 58, a narrow aperture 59, radial bores 60 in the sleeve 54, an opening 61 and a bore 62 to the control chamber 34. In the control chamber 34, the entire operating surface 63 of the control piston 19 is acted upon by the compressed air. As a result, the sealing lip 31 of the seal 24 is pressed against the end surface 30 of the sleeve 8 and a sealing effect is obtained. The operating piston 39 is located at its uppermost position and is held there with the sealing lip 32 of the sealing member 24 exerting a gripping action on the upper collar 64 of the operating piston 39.

To effect a nail-driving stroke, the parts of the tool are moved into the positions shown in FIG. 2 by moving the valve rod 53 with the assistance of the trigger 55. In this position, the O-ring 57 blocks the admission of compressed air from the piston-grip chamber 4 to the control chamber 34. At the same time the O-ring 65 has moved into a position in which it permits communication with the atmosphere, so that the compressed air is able to escape from the control chamber 34 by way of the bore 62, the opening 61, the narrow aperture 59, a further narrow aperture 66 and a duct 67 to the atmosphere. Consequently the control chamber 34 is now at atmospheric pressure. In this condition it is possible that compressed air infiltrating past seals 27 from the differential chamber 29 may flow via duct 29a and past sealing ring 28 into the control chamber 34. The compressed air acting on the annular surface 68 of the control piston 19 is now able to displace the control piston 19 upwards until the end surface 69 of the protrusion 22 contacts the seal 35. Immediately following lifting of the sealing lip 31 from the end surface 30, the sealing lip 32 is exposed to the compressed air and produces an increased gripping action on the collar 64 of the piston. The operating piston 39 is then also raised a distance corresponding to the stroke of the control piston 19. Only after the control piston 19 has moved into a position in which its end surface 69 is against the seal 35, i.e., when the outlet aperture is closed, does pressure build up in the space 26, compressed air flowing in from the pistol-grip chamber by way of the opening 20, a narrow passage 70 leading from the groove 41a, the bore 47 and the channel 46. During this movement of the control piston, the O-ring 41 is displaced by the compressed air into its lower sealing position. Immediately the pressure which accumulates in the space 26 and acts on the end surface 71 of the operating piston 39 overcomes the gripping action of the lip 32, the operating piston 39 is urged away from its terminal position. The compressed air flowing past the periphery of the piston can now operate on the upper surface 71 of the piston without any fall in pressure as it proceeds through the inlet chamber 72 which is now completely open.

In the condition shown in FIG. 3, the piston has finished its downward travel. In this position, compressed air is flowing by way of the opening 73 and the bores 17 into the chambers 16 and 16a to effect return movement of the piston, air being able to pass from the latter chamber into an annular space 76 through the bores 18. During the downward travel of the operating piston 39, the latter has displaced the air located beneath it through the bores 17 and 18 into the chambers 16 and 16a. This air now attempts to expand and it enters space 76 via the bores 18 and returns the operating piston 39 towards its original position.

In the position shown in FIG. 4, the trigger 55 is no longer being actuated, so that the valve rod 53 returns to its initial position as shown in FIG. 1. Compressed air can thus once more enter the control chamber 34, and the control piston 19 returns to its initial position as shown in FIG. 1. In this lower sealing position of the control piston 19, the end surface 69 moves away from the seal 35 to open the outlet 37, and the compressed air located in the cylinder chamber 50 is able to escape to atmosphere. The compressed air from chambers 16 and 16a, acting on the under-side 74 of the piston 39, is now able to urge the operating piston 39 into its initial position as shown in FIG. 1 in which it is held by the pre-stressed lip 32. The pressure remaining in the chambers 16, 16a and 50 after the return stroke of the operating piston is still above atmospheric pressure and this pressure is able to displace the O-ring 41 in the groove 41a of the operating piston 39. The O-ring 41 is moved into an annular extension 48 of the working cylinder 5, with the result that an annular opening 75 is created on its rearward side (FIGS. 1 and 2). The remaining compressed air is now able to escape to atmosphere by way of the space 76, the opening 75, the bore 47, the groove 46 and the bores 26 and 37. The tool is thus prepared for the next driving operation.

Claims

We claim:

1. In a compressed air operated driving tool for fasteners comprising, in combination, a casing having a cylindrical working cylinder, an operating piston reciprocal within said working cylinder movable between a normal retracted position and an extended working position, a control piston within said casing concentrically related to said working cylinder and located adjacent said operating piston when said piston is in said retracted position and having oppositely disposed first and second pressure faces of unequal area, a reservoir in said casing connected to a compressed air supply, a passage in said casing establishing communication between said reservoir and said control piston first face, a control valve on said casing selectively venting said control piston second face to the atmosphere, sealing means on said control piston sealing said working cylinder from said reservoir when said operating piston is in the retracted position, an annular holding surface on said operating piston, and an annular resilient sealing lip on said control piston concentric with said holding surface frictionally engaging said holding surface to maintain said operating piston in the retracted position, actuation of said control valve displacing said control piston axially from said operating piston releasing said operating piston and exposing said operating piston to said compressed air supply in said reservoir whereby said operating piston is moved to said extended position.

2. In a compressed air operated tool as in claim 1 wherein said sealing means and said annular resilient sealing lip are integrally formed on a common annular member supported within said control piston.

3. In a compressed air operated tool as in claim 1, a cushioning air chamber in said casing in communication with said working cylinder on the side of said operating piston remote from said control piston whereby said operating piston compresses air within said chamber during extension, and said compressed air in said chamber returns said operating piston toward said control piston.