EP0152376A1 - Percussion device - Google Patents

Abstract

The percussion mechanism of this apparatus, comprising a cylinder (1), a free piston (6), an anvil (18), a tool holder (19) in which is disposed a bundle of needles (21) whose heads (21a) are intended to be applied against the anvil (18), is slidably mounted in a tubular casing (10) between two springs (20, 22) serving to dynamically isolate this percussion mechanism from this casing (10) and from the handle (14) which serves to hold it. The cylinder (1) is mounted in this housing by a suspension made up of two annular seals (11) and this cylinder is adjusted with a clearance so that the centering imparted by the seals (11) mechanically isolates this cylinder from the housing and reduces the transmission of vibrations.

Description

The present invention relates to a percussion device corrprenant a housing elongated in the front end of which a metal needle bundle axially protrusion, a door _- needles longitudinally slidably mounted within said housing, a spring for resiliently pressing this needle holder against an anvil, a cylinder mounted longitudinally sliding inside said casing and the front end of which serves as a rear stop for this anvil and is open to allow axially a free piston mounted in this cylinder and jpuant the role percussion member, motor means for initiating and maintaining a series of percussion at a given frequency of said percussion member against said anvil and an elastic compression element disposed between the respective rear ends of this casing and of this cylinder.

Such devices are used for the stripping of surfaces and for this purpose comprise a bundle of metal needles. Other devices of the same type have a chisel and are used for example to remove the weld bead which projects at the junction of two parts, to remove burrs etc. Prolonged use of these devices is annoying because of the noise and due to the vibrations of the device.

There is another type of percussion device, it is a device without anvil or free piston, but with two coaxial pistons pressed against each other by two springs and spreading one of the 'other then approaching alternately under the effect of a pneumatic motor mechanism. Such a device is relatively silent, but is limited to low powers and its performance with respect to the flow of compressed air consumed is quite poor. Given their low power, these devices cannot be used for work such as pickling rusty sheets or attacking concrete surfaces.

It has already been proposed to attenuate the vibrations generated by impact tools, in particular the vibrations transmitted to the casing and to the gripping members of the tool and which result in increased fatigue for the user and therefore in efficiency. less during prolonged use. This is particularly the case of FR-A-1,059,349 in which a cylinder is mounted longitudinally sliding between two springs in a casing secured to a handle. A longitudinally sliding mounting between two springs is also illustrated by FR-A-1,154,429 and by US-A-3,788,404. This elastic mounting in the longitudinal direction of the percussion mechanism in the casing should normally make it possible to obtain a very noticeable vibration damping effect insofar as the free piston of the percussion mechanism moves loazgitudinally. However, the vibrations being transmitted to the housing by all the contact surfaces, in particular by the guide surfaces of the sliding mechanism in the housing. However, this guiding must be carried out with sufficient precision, failing which, the wear between the moving parts increases rapidly and also results in overheating and swelling of the casing which is thus quickly put out of use.

The elastic mounting of the aforementioned solutions is also limited to pneumatic tools supplied axially with compressed air from the rear end. This feeding method is not suitable for small hand-held devices such as needle guns or pneumatic chisels. These devices have a side handle, hence their name "pistol", and it is therefore much more practical to feed the striking mechanism laterally by the handle. However, this lateral supply supposes a perfect seal between the casing and the striking mechanism, so that this presupposes close contact between the vibration generating mechanism and the casing.

The object of the present invention is precisely to provide a solution which makes it possible to effectively reduce the vibrations transmitted to the casing in this type of device, while retaining in particular the convenience of the supply of lateral compressed air by the handle.

To this end, the subject of the present invention is a percussion device of the aforementioned type as defined by claims 1 and 2.

The advantage of this device lies in a considerable damping of vibrations. However, the measures taken to increase this depreciation do not entail costly modifications to the device, or structural or operational corrections. The solution object of this invention practically does not interfere with the motor mechanism and therefore does not reduce the initial useful power of the device, contrary to what has been proposed in the case of devices in which the tool is integral with a reciprocating piston.

Other advantages will become apparent in the light of the description which follows and of the appended drawing which illustrates schematically and by way of example, two embodiments and a variant of the apparatus which is the subject of the invention.

• Fig. l is a sectional elevation view of this first embodiment.
• Fig. 2 is a visible view of the second embodiment.
• Fig. 3 is a sectional view along line III-III of FIG. 2.
• Fig. 4 is a partial sectional view of a variant of FIG. 1.
• Fig. 5 is a detail view greatly enlarged along the circle in phantom line V of FIG. l.
• Figs 6 and 7 are two acceleration diagrams.

The apparatus illustrated in fig. l comprises a cylinder 1, the front end of which is open and the rear end of which is closed by a plug 2 held in place by an elastic ring 3. This cylinder 1 has two compartments 4 and 5. A free piston 6, having a front section 6a of small diameter and a section 6b of large diameter, is slidably mounted inside this cylinder. It comprises a T-shaped duct 7 having an axial part 7a extending from the rear face of the free piston 6 to a diametrical part 7b. A light 8 places the compartment 4 of the cylinder 1 in communication with an annular space 9 formed between the cylinder 1 and a casing 10 in which this cylinder is mounted axially sliding. This annular space is sealed by two annular seals 11 arranged in the cylinder 1 on either side of this annular space 9. Another light 12 passes through the wall of the casing 10 and serves to communicate the annular space 9 with a supply duct 13 passing longitudinally through a handle 14 fixed laterally to the casing 10 and giving the device the appearance of a gun. This supply duct 13 is intended to be connected to a source of compressed air (not shown). A lever 15 articulated around a transverse axis 16 to the handle 14 is used to control the opening and closing of a valve 17 controlling the supply duct 13.

The open front end of the cylinder 1 is in contact with an anvil 18 against the front face of which a tool holder 19 is pressed by a spring 20 which bears against a narrowing 10a of the diameter of the casing 10. The tool holder 19 carries a bundle of needles 21 of which only one needle is shown, intended for the etching of surfaces. The needles 21 are freely mounted through the tool holder 19 and have a head 2la intended to come into contact with the front face of the anvil 18 when the tool is applied against a surface to be worked.

The rear end of the cylinder 1 is biased by a spring 22 compressed between this cylinder and the rear end of the casing 10.

In order to reduce the transmission of vibrations to the casing 10, the diameter of the cylinder 1 is dimensioned so as to fit in this casing with sufficient clearance so that there is no contact between this cylinder and the casing. In this example, the clearance is 0.2 mm over the diameter. The centering of the cylinder 1 and its suspension in the casing are ensured by the seals there which therefore serve two purposes. For this purpose, these seals have a Z-shaped section so as to make the suspension of the cylinder sufficiently elastic and to absorb as much as possible the vibrations transmitted to the casing 10. A partial view in very enlarged section of the detail of the elastic suspension of the cylinder 1 in the casing 10 is illustrated in FIG. 5. Since the casing and the cylinder are separated from each other, the internal surface of the casing 10 does not need to be treated by case hardening, which constitutes a saving in manufacturing cost. Among the advantages of this embodiment, it can also be noted that the proposed solution lends itself particularly well to the lateral supply of compressed air which constitutes the least expensive solution. Furthermore and contrary to the a axial supply, the cylinder 1 and the supply duct 13 have no mechanical connection so that the cylinder cannot be subjected to stresses making an angle with the longitudinal axis of the device as this occurs with the supply axial when the supply duct is off-center.

It should also be noted that the needle holder 19 is preferably made of plastic as described in US-A-4,134,193, while the surface of the anvil 18 in contact with the casing 10 is also preferably made of plastic as described in Swiss Patent No ....... (dde No 5 962 / 83-0). Therefore, the housing 10 is not in contact with any metal part of the percussion mechanism.

When using the device, the front end of the needles 21 is applied against the surface to be worked, so that their heads 2la come into contact with the front face of the anvil 18. Depending on the pressure exerted, the spring 22 is more or less compressed. By opening the valve 17 controlling the supply duct 13 by depression of the lever 15 against the handle 14, the compressed air is brought into the compartment 4 of the cylinder 1. Thanks to the T duct 7, this air is brought between the face rear of the free piston 6 and the rear end of the compartment 4, the bottom of which is constituted by the shutter plug 2. This results in a displacement of the free piston 6 forwards in the direction of the anvil 18, against the rear face which this piston hits. In this position, the rear part of compartment 4 is no longer in contact with the pressurized air supply, but with compartment 5 open towards the front so that the pressurized air being in the rear part from compartment 4 escapes. As the front part of this same compartment 4, constituted by an annular space formed around the small diameter front section 6a of the free piston 6 remains in contact with the source of air under pressure, the pressure rises in this annular space and brings the piston 6 back, after which the cycle begins again.

As can be seen, the presence of the spring 22 does not in any way interfere with the operation of the free piston engine mechanism. This spring 22 is compressed as a function of the pressure exerted to apply the tool or tools 21 against the surface to be worked. On the other hand, the vibrations due to the shock of the free piston 6 against the anvil 18 and that of the tools 21 against the working surface are absorbed by the springs 20 and 22 between which the seat of the mechanism is mounted in the casing 10. In addition, the absence of any rigid connection between the striking mechanism and the casing 10 has the effect that these vibrations are practically not transmitted to this casing and to the handle 14, thus considerably reducing the fatigue of the user, without significantly reducing the efficiency of the device. This improvement does not lead, moreover, to a noticeable increase in the cost price since it requires only an additional spring, the presence of which does not affect the cost of assembly, compensated for by the fact that the inside of the casing 10 must not be case-hardened.

The variant illustrated in FIG. 2 relates to a device with a single tool consisting of a chisel 23 and a percussion mechanism identical to that of FIG. l and which, therefore, will not be described. In this variant, the chisel 23 is directly in contact with the free piston 6. The rear part of square section is slidably mounted in a guide member 24 fixed to the front end of the cylinder 1 and the chisel is held in place by a cap 25 hooked at the front end of the guide member 24 and to a flange 23a formed on this chisel 23. The guide member 24 also has two openings 26 for the exhaust of air leaving the cylinder 1. The front end of the spring 20 bears against a ring 27 secured to the casing 10. Finally, to prevent the entire mechanism from rotating in the casing 10, the latter has two stamped projections 28 cooperating with two grooves 29 of the member guide 24, cam illustrated in particular by FIG. 3. These features aside, this device is similar to that of FIG. 1 both by design and by operation. Cn will therefore refer to the description relating to this figure 1 to know the ensble of the mechanism and its operation.

The variant illustrated in FIG. 4 shows an apparatus whose casing 10 is surrounded over a part of its length by a tubular element 30. An acoustic absorbent material, such as a plastic foam 31, in particular a polyurethane foam, fills the space between these tubular elements and is in contact with inside the casing 10 thanks to openings 32. This acoustic insulating casing makes it possible to dampen the parasitic vibrations which could remain in the area of the anvil 18 and of the needle holder 19. Such vibrations result from non-longitudinal components generated following the striking action of the free piston 6 on the anvil 18. Such a tubular acoustic insulating element therefore compièces the action of the damping springs and the suspension of the cylinder 1, further reduces the level of residual vibrations and decreases the effect of the noise generated by the repeated shock of the free piston 6 on the anvil 18.

The apparatus which is the subject of the invention has been subjected to a series of comparative tests at the "Federal Laboratory for Materials Testing and Research Institute" in Dubendorf (Switzerland), as well as at the "Institit für Hygiène und Arbeitsphysiologie "from the Federal Polytechnic in Zurich. The tests related, on the one hand, to comparative measurements of accelerations and, on the other hand, to physiological tests relating to the effects of various devices including that which is the subject of the invention, on individuals who had kept in ignorance of the nature of the tests in which they participated, in order to avoid the influence of psychological factors. Figures 6 and 7 show two diagrams of the accelerations measured in the band from 3 Hz to 1000 Hz on the device object of the invention, respectively on an identical device but devoid of elastic suspensions.

The physiological tests were carried out using the device which is the subject of the invention and three other devices, all of the needle pistol type, one of the comparison devices being sold by the holder of the invention on the market. and the other two being sold by other manufacturers.

These tests focused on the acceleration of heartbeats, following the use of the devices, which is around an increase of 35 pulses / min. for the three comparison devices, while this acceleration is 25 pulses in the case of the device object of the invention. The tests were carried out with ear protection against noise in all cases, without this protection, there is still a uniform increase of 15 additional pulses.

The increase in surface temperature was also measured at the fingertips after use of the device. It is 3-4 ° C for the three comparison devices and 2 ° C for the device according to the invention.

The force required by the flexor muscles of the hand was recorded by the electrical activity of these nuscles which is a linear function of the force developed. It can be seen that in the case of the device according to the invention, this force represents only 80% of the force required in the case of the lightest of the three comparison devices which is even lighter than the device according to the invention (3.070 kg versus 3.220 kg respectively).

Another test carried out is the increase in the reflex time of the biceps after work, while this increase is 3 ms in the case of the device according to the invention, it is from 8 to 13 ms for the three devices of compaison.

Tests relating to the sensitivity of touch have shown that the decrease in sensitivity is 50% lower following the use of the device which is the subject of the invention.

Other subjective data recorded in questionnaires with people who participated in these comparative tests confirmed the recorded data.

It can therefore be seen that all of the physiological tests carried out show a marked improvement in the conditions of use of the percussion device which is the subject of the invention on devices currently on the market and which do not have vibration damping between the impact mechanism and housing.

It may also be mentioned here that the shape of the annular suspension seals 11 with an annular Z-shaped straight section has proved to be extremely important insofar as it makes it possible to produce an effective seal and a suspension which is sufficiently elastic to absorb vibrations. Indeed, the replacement of these seals by 0-rings with a full circular section has made it possible to note an already significant reduction in the vibration damping effect.

Claims (4)

1. Percussion device comprising an elongated casing at the front end from which a bundle of metal needles protrudes axially, a needle holder mounted longitudinally sliding inside this casing, a spring for resiliently pressing this needle holder against an anvil, a cylinder mounted longitudinally sliding inside said casing and the front end of which serves as a rear stop for this anvil and is open to allow axially a free piston mounted in this cylinder and playing the role of percussion member , motor means for initiating and maintaining a series of percussions at a given frequency of said percussion member against said anvil and an elastic compression element disposed between the respective rear ends of this casing and of this cylinder, characterized in that the diameter of this cylinder is chosen to give an adjustment with clearance inside the casing, two elastic annular bearings, spaced long itudinally from one another, being interposed between this cylinder and the casing to guide this cylinder coaxially inside this casing and serve as a suspension between these members. 2. Percussion device having an elongated casing at the end before which a tool holder receives a tool which projects axially and is mounted longitudinally sliding in this tool holder, this casing containing a cylinder mounted longitudinally sliding at the inside of said casing and the front end of which is adjacent to the tool holder and is open to allow a free piston axially mounted in this cylinder to pass axially and acting as a percussion member of the tool, motor means for initiating and maintaining a series of percussions at a given frequency of said percussion member against said tool and two elastic compression elements disaosed at the two respective ends of this casing by exerting their opposing forces on the cylinder, characterized in that the diameter of this cylinder is chosen for give an adjustment with play inside the casing, two elastic annular bearings, separated longitudinally from each other, being interposed between this cylinder and the casing to guide this cylinder coaxially inside this casing and serve as a suspension between these members. 3. Percussion device according to one of claims 1 and 2, characterized in that the housing is surrounded on at least part of its length by a tubular element, a vibration damping material being disposed between this element and the housing . 4. Apparatus according to one of claims 1 and 2, characterized in that said cylinder has a lateral opening intended to communicate with an annular space in which opens a supply duct intended to be connected to a source of pressurized air, said annular bearings being arranged on either side of this annular space to seal it, the cross section of these bearings having the shape of a Z, the parallel branches of which respectively bear against the casing and in the bottom of an annular groove formed in the wall of said cylinder.

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