Handle assembly for tool

A power sander (2) having a housing (4) and a motor within the housing is disclosed. A gripping portion adapted to be engaged by a hand of a user of the sander comprises blister packs (30), (36) comprising first and second flexible sheets defining a gel-containing chamber therebetween and containing a vibration damping gel material, the first and second sheets being sealed to each other at the periphery of each gel-containing chamber. Clamping plates (34), (40) include a body portion and pins (not shown) adapted to extend through the periphery of a corresponding blister pack and to protrude inwardly of the surface of the housing (4). The pins are then deformed by means of heat or ultrasound to secure the clamping plates (34), (40) to the housing (4).

FIELD OF THE INVENTION

The present invention relates to handle assemblies for tools, and relates particularly, but not exclusively, to handle assemblies having combined friction gripping and vibration damping properties, for power tools in which an output shaft is driven by a motor.

BACKGROUND OF THE INVENTION

Known power tools, such as power drills in which a drill bit is rotated by an output shaft which is in turn rotated by means of an electric motor, generate significant amounts of vibration, which can under certain circumstances limit the length of time during which the tool can be used continuously. In addition, the housing of such tools is generally made from a durable plastics material on which it can be difficult for a user of the tool to maintain a grip when the tool is in use for a sustained period.

U.S. Pat. No. 6,308,378 discloses a gripping arrangement for a handle of a power tool in which the sides of the handle are provided with frictional gripping zones, each side of the handle including a plurality of alternating gripping zones of a softer material and a harder material. The softer material used is generally a thermoplastic elastomer or rubber material, and the harder material is generally the same material as that from which the tool housing is formed.

This known arrangement suffers from the drawback that because the softer material performs the dual functions of providing a friction grip and vibration damping, the choice of material constitutes a compromise in that although it will have acceptable friction reducing and vibration damping properties, the performance of the handle is limited because a material having optimum frictional properties will generally have unacceptable vibration damping properties, and vice versa.

WO02/38341 discloses a grip handle for a hand-held machine tool in which a hand grip is separated from the remainder of the housing by a vibration damping element consisting of an inflatable annular air filled cushion. An additional handle is provided which has a tubular grip element surrounding a further annular air cushion.

This known arrangement suffers from the drawback that the vibration damping properties of air can only be varied by adjusting the air pressure within a chamber containing the air, and even then, the range of vibration damping properties achievable is limited. Furthermore, it is difficult, and therefore expensive, to manufacture a sealed chamber containing air having a predetermined pressure.

Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided a gripping portion for a power tool having a housing and a motor within said housing for actuating a working member of the tool, the gripping portion adapted to be engaged by a hand of a user of the tool and comprising:

at least one blister pack comprising first and second flexible sheets defining at least one gel-containing chamber therebetween, wherein the or each said gel-containing chamber contains a vibration damping gel material and said first and second sheets are sealed to each other at a sealing portion at the periphery of the or each said gel-containing chamber; and

at least one fixing member for fixing at least one said blister pack to said housing and including a body portion and (i) at least one protrusion extending from said body portion and adapted to extend through a sealing portion of a said blister pack and engage a respective first aperture in the housing, and/or (ii) at least one second aperture in said body portion for engaging a respective protrusion on said housing and extending through a sealing portion of a said blister pack.

By providing at least one fixing member for fixing at least one said blister pack to said housing and including a body portion and (i) at least one protrusion extending from said body portion and adapted to extend through a sealing portion of a said blister pack and engage a respective first aperture in the housing, and/or (ii) at least one second aperture in said body portion for engaging a respective protrusion on said housing and extending through a sealing portion of a said blister pack, this provides the advantage of minimising the risk that the blister pack becomes detached from the handle portion and minimising the risk of inadvertent or unauthorised removal of the blister pack from the handle portion.

At least one said sealing portion may include at least one third aperture to enable a respective said protrusion to pass therethrough.

In a preferred embodiment, at least one said protrusion is provided on at least one said fixing member and is adapted to protrude from a respective said first aperture on side thereof remote from the corresponding said body portion.

The protrusions and or second apertures may be irregularly spaced.

This provides the advantage of minimising the risk of incorrect assembly of the gripping portion.

According to another aspect of the present invention, there is provided a power tool comprising:

a housing having at least one first aperture;

a motor within said housing for actuating a working member of the tool; and

a gripping portion as defined above;

wherein at least one said fixing member includes at least one said protrusion fixed to a corresponding said first aperture in said housing.

At least one said protrusion may be fixed to the corresponding said second aperture by means of deformation of an end of said protrusion remote from the corresponding said body portion.

An end at least one said protrusion may be deformed by means of heat.

An end of at least one said protrusion may be deformed by means of ultrasound.

The tool may be a sander.

According to a further aspect of the present invention, there is provided a method of assembling a gripping portion for a power tool, the method comprising:

locating at least one fixing member having a body portion and at least one protrusion extending from said body portion on a housing of a power tool having at least one first aperture such that at least one said protrusion passes through a sealing portion at the periphery of a blister pack containing vibration reducing gel material, and engages a respective said first aperture; and

deforming an end of at least one said protrusion remote from said body portion to fix the protrusion to the corresponding said first aperture.

The method may further comprise the step of locating at least one said blister pack on at least one said fixing member, such that at least one said protrusion extends through the sealing portion of at least one said blister pack, prior to location of said fixing member on said housing.

The step of deforming an end of at least one said protrusion may comprise deforming by means of heat.

The step of deforming an end of at least one said protrusion may comprise deforming by means of ultrasound.

Referring toFIGS. 1 to 9, a power sander2has a housing4supporting a mounting platen6for supporting a sanding head8(FIG. 10) for oscillatory orbital motion of the platen6and sanding head8relative to the housing4. The housing4has side surfaces10,12, a curved front surface14containing an on/off switch16for switching electrical power to a motor18(FIG. 10) in the housing4, a curved upper surface20and a generally saddle shaped graspable surface22located between the front surface14and upper surface20. The graspable surface22has a concave upper portion24and concave side portions26,28arranged on opposite sides of the upper portion24.

DETAILED DESCRIPTION OF THE INVENTION

For ergonomic handling of the sander by a user, the saddle shaped graspable surface22has a concaved upper portion24having a radius of curvature of about 23 mm, and side portions26,28having radii of curvature of about 10 mm.

The upper surface20of the housing4is defined by a blister pack30, defining a gel-containing chamber32containing vibration absorbing gel formed from a semi solid silicone rubber or polyurethane material and protruding from an aperture in a clamping plate34. Similarly, each side surface10,12is defined by a blister pack36, defining a gel-containing chamber38protruding through an aperture in clamping plate40. It can therefore be seen that the external surface of the sander2to be gripped by a user is defined by the gel-containing chambers32,38of blister packs30,36respectively, and the clamping plates34,40, so that the amount of vibration transmitted to a user's hand is reduced by means of the gel material contained in the blister packs30,36.

As shown in greater detail inFIGS. 9A and 9B, the blister pack36forming part of side surface10is formed from a pair of flexible sheets46of polyurethane material defining gel-containing chamber38and sealed together at a peripheral portion48surrounding the gel-containing chamber38. The peripheral portion contains no vibration absorbing gel material and is pierced by a series of apertures44which correspond in position to apertures42on the part of housing4to which the blister pack36is to be mounted, and to pins43moulded onto the rear surface of clamping plate40. The blister pack36is mounted to the housing4by passing the pins43of clamping plate40through the corresponding apertures44in the peripheral portion of blister pack36, and then inserting the pins43into the corresponding apertures42on the housing4. In particular, the blister pack36is located on the pins43of clamping plate40, and the pins of the clamping plate40are then located in the apertures42on the housing. The pins43and apertures42,44are irregularly spaced, which minimises the risk of incorrect location of the clamping plate40, blister pack36and housing4relative to each other.

The pins43on clamping plate40are of such length that when the blister pack36is located on the pins and the clamping plate40is mounted to the housing4by locating the pins in apertures42on the housing4, the pins protrude from the inner wall of the housing4to a depth of approximately 3 mm. The clamping plate40is then sealed to the housing4by a technique known to persons skilled in the art as “hot staking” in which a heated mandrel is applied to the protruding ends of the pins, which melts the protruding ends so that they are widened in a generally circular arrangement and fix the pins to the housing4in a manner similar to that of a rivet. Alternatively, the distal ends of the pins can be heated by means of ultrasound. The clamping plate40is then sealed to the housing and prevents removal of the clamping plate40from the housing4, and the gel-containing chamber38of blister pack36protrudes through the aperture45of clamping plate40to define part of side surface10, while removal of the blister pack36is prevented because the pins pass through the apertures44in the blister pack36.

Similarly, the blister pack36forming part of opposite side surface12and the blister pack30forming part of upper surface20are secured to the housing in a similar manner by means of heat or ultrasound.

FIG. 10shows a drive unit including the electric motor18and first drive shaft50. A fan52mounted on shaft50is arranged to draw air in from mouth54of the drive unit as shown by arrow A (FIG. 11), and direct it through extractor duct56to outlet58, as shown by arrow B. Bearing60is eccentrically located radially in respect to shaft50, and a second drive shaft62rotates about the axis of bearing60. Mounting platen6is fixed to the housing4by means of four flexible rubber legs64. The mounting platen6is substantially flat, and the legs64extend from a common major surface of the platen6(the upper surface as shown inFIG. 10), directed into the body of the housing4. The flexible legs64extending from the mounting platen6are permanently fixed at their housing end to the housing4, i.e. they are not removable in use by the operator. They are attached to the housing4by means of clamping flanges66of the housing4. The flexible legs64are attached at their mounting platen end to the mounting platen6by passing through apertures in hollow projecting portions68that extend in the direction of the flexible legs64from the upper surface of the mounting platen6. The flexible legs64are provided at their mounting platen6end with an internally screw threaded hollow recess for attachment to a securing screw. The manner in which this securement to the mounting platen is effected is described in more detail below with reference toFIG. 11.

The mounting platen6surrounds the second drive shaft62, and is spaced radially therefrom. This means that the mounting platen6itself is not directly driven by either of the drive shafts.

InFIG. 10a first sanding platen, which is a random orbit sanding head8, is secured next to the mounting platen6onto the drive shaft62. Securement of the random orbit sanding head8is achieved by a bolt70and washer72. The bolt70passes through an aperture in the sanding head8, through aperture74in the mounting platen (seeFIGS. 12 and 13), and over the driving spindle of the second drive shaft62. The sanding platen8is located in a parallel plane to the mounting platen6, but is spaced from it, so that there is no contact between the facing surfaces of the mounting platen6and the sanding shoe8. Therefore free rotation of the sanding platen8is permitted about the bearing axis60, and the platen8exhibits a random orbit.

A brake pad76is provided on the under-surface of the mounting platen6. The brake pad76comprises a resilient member78in the form of a ring formed from a synthetic rubber resilient material, and an abrasion resistant contact layer80comprising polytetrafluoroethylene (PTFE) filed with carbon fibre or glass for increased abrasion resistance. The arrangement of the layers is such that when the sanding platen8is secured in place onto the drive62then the resilient ring78is under compression so that a resultant load is put by the filled PTFE layer80onto a reaction surface part82of the underlying upper surface of the sanding platen8. The purpose of this brake76is two-fold: first, in use, the brake acts as a speed limiter, operating in particular to prevent scratches when the unit is placed on and taken off the work surface, and secondly when the unit is switched off, the stop time is very much reduced compared to a non-braked tool. In operation the drive shaft50is typically driven at a rotational speed of 12000 rpm, which is too fast a speed for rotation of the sanding platen8. The brake pad76limits the rotational speed of the platen to an acceptable operating speed, typically around 1200 rpm, or 10% of the rotational speed of the motor.

FIG. 11shows the drive unit of the hand tool with an orbital sanding platen84mounted in place of the random orbit platen ofFIG. 10. AlsoFIGS. 12 and 13are perspective views of the mounting platen8(which is common to bothFIGS. 10 and 11) and the sanding platen84(which is shown inFIG. 11, but not inFIG. 10).

FIGS. 12 and 13show in more detail features of the mounting platen8, which remains on the housing when the platens84and8are interchanged. From these Figures it can be seen that the mounting platen8is generally a blunt shoe shape, and is substantially flat, with a peripheral lip86extending downwards towards the sanding shoe84. The large central aperture74, allowing it to be positioned around the second drive shaft, radially distant therefrom, so there is no direct contact between the mounting platen6and the second drive shaft62, can also be clearly seen in these Figures, as can the four hollow right cylindrical portions88, integrally formed with the surface of the mounting platen8, and projecting into the body of the housing4i.e. upwards as shown in the Figures. An inner lip90extends downwards around most of the central aperture74, and joins to the outer peripheral lip92of the mounting platen6at two points94on one short side of the mounting platen8.

In line with the upwardly directed projections88, and projecting in the other direction, from the opposite surface of the mounting platen6are four hollow, generally cylindrical pin shaped coupling members96. The pin-shaped coupling members96are also integrally formed with the mounting platen8. The substantially flat mounting platen with its projecting portions88and96are preferably integrally injection moulded from polymeric material or diecast zinc.

The four coupling pins96, provided on the opposite surface of the mounting platen6from the flexible legs64, in corresponding positions, i.e. vertically aligned with the legs64as shown inFIGS. 12 and 13have a dual function; the pins96secure the legs64in place, and couple with an orbital sanding head84, in use, to prevent free rotation of that sanding head (FIGS. 11 to 13).

Each coupling pin96is an integrally formed part shaped as a hollow cylinder. The pin member96contains a radially directed flange98extending partially into the hollow of the pin member96, to act as a stop member for a separate externally screw threaded headed bolt member100(seeFIGS. 10 and 11). The externally screw threaded bolt member100passes through the hollow central pin member96, and is shaped and sized to slide into the hollow pin member until its head abuts the internal stop flange98, and then screw into inner hollow screw threaded cylindrical recesses at the mounting platen end of the flexible legs64. By this screw threaded bolt member100the flexible legs64are therefore secured to the mounting platen.

As best seen inFIG. 11, each pin member96is located between part of the peripheral lip86and the inner lip90of the mounting platen6. The pin member96of the coupling means acts to couple to the orbital sanding shoe84to prevent its free rotation.

As shown inFIG. 11, when mounted on the drive unit, the orbital sanding shoe84is secured to the spindle of second drive shaft62by means of the same nut70and washer72used to secure the random orbit sanding platen8ofFIG. 10. The orbital sanding shoe84is substantially flat, and is provided, on its upper major surface in the orientation shown in the Figure, with coupling means92shaped to co-operate with the coupling means96of the mounting platen6. The coupling means92each comprise a hollow right-cylindrical stub, projecting upwards from the surface of the sanding shoe84. The hollow right cylindrical projection92is shaped so that it provides a recess into which the pin member96of the mounting platen fits. One side of the cylindrical projection92on the sanding shoe84fits between the peripheral lip86of the mounting platen6and the outer surface of the pin member96of the mounting platen6; and the opposite side of the cylindrical projection92on the sanding shoe84fits between the inner lip90of the mounting platen6and the opposite outer surface of the pin member96of the mounting platen6.

By means of the co-operating coupling means96and92, the sanding shoe84and mounting platen6are therefore securely located substantially to prevent relative movement between the mounting platen6and the sanding shoe84in a plane perpendicular to the axis of the bearing60. Relative movement parallel to the axis of the bearing60is, of course, prevented by the nut70and washer72attachment.

In operation, when the motor is switched on and the drive shafts50and62turn, since the sanding shoe84is prevented from rotation relative to the mounting platen6, and the mounting platen6is fixed relative to the housing4by means of legs64, then free rotation of the sanding shoe84around the bearing60axis is prevented. The flexibility in the legs64, however, allows the sanding platen84to follow the rotating motion of the eccentric spindle itself driven by the first drive shaft50. Therefore the sanding shoe84is allowed to oscillate within a fixed orbit due to the flexibility of the legs64.

In order to ensure that the sanding shoe84is always located the correct way round on the mounting platen6, the coupling means96and92are non uniformly spaced over the surface of the mounting platen6and the sanding platen84, those on one lateral side of the platens (the right as shown inFIGS. 12 and 13) being further apart from each other than those on the other lateral side of the platens (the left as shown in the Figures).