Patent Abstract:
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 ).

Full Description:
FIELD OF THE INVENTION  
       [0001]     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  
       [0002]     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.  
         [0003]     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.  
         [0004]     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.  
         [0005]     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.  
         [0006]     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.  
         [0007]     Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     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:-  
         [0009]     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  
         [0010]     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.  
         [0011]     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.  
         [0012]     At least one said sealing portion may include at least one third aperture to enable a respective said protrusion to pass therethrough.  
         [0013]     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.  
         [0014]     The protrusions and or second apertures may be irregularly spaced.  
         [0015]     This provides the advantage of minimising the risk of incorrect assembly of the gripping portion.  
         [0016]     According to another aspect of the present invention, there is provided a power tool comprising:-  
         [0017]     a housing having at least one first aperture;  
         [0018]     a motor within said housing for actuating a working member of the tool; and  
         [0019]     a gripping portion as defined above;  
         [0020]     wherein at least one said fixing member includes at least one said protrusion fixed to a corresponding said first aperture in said housing.  
         [0021]     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.  
         [0022]     An end at least one said protrusion may be deformed by means of heat.  
         [0023]     An end of at least one said protrusion may be deformed by means of ultrasound.  
         [0024]     The tool may be a sander.  
         [0025]     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:-  
         [0026]     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  
         [0027]     deforming an end of at least one said protrusion remote from said body portion to fix the protrusion to the corresponding said first aperture.  
         [0028]     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.  
         [0029]     The step of deforming an end of at least one said protrusion may comprise deforming by means of heat.  
         [0030]     The step of deforming an end of at least one said protrusion may comprise deforming by means of ultrasound. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]     Preferred embodiments of the invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which:-  
         [0032]      FIG. 1  is a perspective view of a power sander embodying the present invention;  
         [0033]      FIG. 2  is a top view of the sander of  FIG. 1 ;  
         [0034]      FIG. 3  is a rear view of the sander of  FIG. 1 ;  
         [0035]      FIG. 4  is a front view of the sander of  FIG. 1 ;  
         [0036]      FIG. 5  is a left side view of the sander of  FIG. 1 ;  
         [0037]      FIG. 6  is a right side view of the sander of  FIG. 1 ;  
         [0038]      FIG. 7  is a detailed rear view of a top surface of the sander of  FIG. 1 ;  
         [0039]      FIG. 8  is a detailed side view of the surface of  FIG. 7 ;  
         [0040]      FIG. 9A  is an exploded perspective view of the housing and gripping portion of the sander of  FIG. 1  from the right side;  
         [0041]      FIG. 9B  is an exploded perspective view of the housing and gripping portion of the sander of  FIG. 1  from the left side;  
         [0042]      FIG. 10  is a side cross sectional view of part of the sander of  FIG. 1 ;  
         [0043]      FIG. 11  is a view, corresponding to  FIG. 10 , of a sander of a second embodiment of the present invention;  
         [0044]      FIG. 12  is a perspective view of a mounting platen and sanding shoe of the sander of  FIG. 10 ; and  
         [0045]      FIG. 13  is a perspective view of the mounting platen and sanding shoe of  FIG. 10 , showing the attachment side of the mounting platen; 
     
    
       [0046]     Referring to FIGS.  1  to  9 , a power sander  2  has a housing  4  supporting a mounting platen  6  for supporting a sanding head  8  ( FIG. 10 ) for oscillatory orbital motion of the platen  6  and sanding head  8  relative to the housing  4 . The housing  4  has side surfaces  10 ,  12 , a curved front surface  14  containing an on/off switch  16  for switching electrical power to a motor  18  ( FIG. 10 ) in the housing  4 , a curved upper surface  20  and a generally saddle shaped graspable surface  22  located between the front surface  14  and upper surface  20 . The graspable surface  22  has a concave upper portion  24  and concave side portions  26 ,  28  arranged on opposite sides of the upper portion  24 .  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0047]     For ergonomic handling of the sander by a user, the saddle shaped graspable surface  22  has a concaved upper portion  24  having a radius of curvature of about 23 mm, and side portions  26 ,  28  having radii of curvature of about 10 mm.  
         [0048]     The upper surface  20  of the housing  4  is defined by a blister pack  30 , defining a gel-containing chamber  32  containing vibration absorbing gel formed from a semi solid silicone rubber or polyurethane material and protruding from an aperture in a clamping plate  34 . Similarly, each side surface  10 ,  12  is defined by a blister pack  36 , defining a gel-containing chamber  38  protruding through an aperture in clamping plate  40 . It can therefore be seen that the external surface of the sander  2  to be gripped by a user is defined by the gel-containing chambers  32 ,  38  of blister packs  30 ,  36  respectively, and the clamping plates  34 ,  40 , so that the amount of vibration transmitted to a user&#39;s hand is reduced by means of the gel material contained in the blister packs  30 ,  36 .  
         [0049]     As shown in greater detail in  FIG. 9A and 9B , the blister pack  36  forming part of side surface  10  is formed from a pair of flexible sheets  46  of polyurethane material defining gel-containing chamber  38  and sealed together at a peripheral portion  48  surrounding the gel-containing chamber  38 . The peripheral portion contains no vibration absorbing gel material and is pierced by a series of apertures  44  which correspond in position to apertures  42  on the part of housing  4  to which the blister pack  36  is to be mounted, and to pins  43  moulded onto the rear surface of clamping plate  40 . The blister pack  36  is mounted to the housing  4  by passing the pins  43  of clamping plate  40  through the corresponding apertures  44  in the peripheral portion of blister pack  36 , and then inserting the pins  43  into the corresponding apertures  42  on the housing  4 . In particular, the blister pack  36  is located on the pins  43  of clamping plate  40 , and the pins of the clamping plate  40  are then located in the apertures  42  on the housing. The pins  43  and apertures  42 ,  44  are irregularly spaced, which minimises the risk of incorrect location of the clamping plate  40 , blister pack  36  and housing  4  relative to each other.  
         [0050]     The pins  43  on clamping plate  40  are of such length that when the blister pack  36  is located on the pins and the clamping plate  40  is mounted to the housing  4  by locating the pins in apertures  42  on the housing  4 , the pins protrude from the inner wall of the housing  4  to a depth of approximately  3  mm. The clamping plate  40  is then sealed to the housing  4  by 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 housing  4  in a manner similar to that of a rivet. Alternatively, the distal ends of the pins can be heated by means of ultrasound. The clamping plate  40  is then sealed to the housing and prevents removal of the clamping plate  40  from the housing  4 , and the gel-containing chamber  38  of blister pack  36  protrudes through the aperture  45  of clamping plate  40  to define part of side surface  10 , while removal of the blister pack  36  is prevented because the pins pass through the apertures  44  in the blister pack  36 .  
         [0051]     Similarly, the blister pack  36  forming part of opposite side surface  12  and the blister pack  30  forming part of upper surface  20  are secured to the housing in a similar manner by means of heat or ultrasound.  
         [0052]      FIG. 10  shows a drive unit including the electric motor  18  and first drive shaft  50 . A fan  52  mounted on shaft  50  is arranged to draw air in from mouth  54  of the drive unit as shown by arrow A ( FIG. 11 ), and direct it through extractor duct  56  to outlet  58 , as shown by arrow B. Bearing  60  is eccentrically located radially in respect to shaft  50 , and a second drive shaft  62  rotates about the axis of bearing  60 . Mounting platen  6  is fixed to the housing  4  by means of four flexible rubber legs  64 . The mounting platen  6  is substantially flat, and the legs  64  extend from a common major surface of the platen  6  (the upper surface as shown in  FIG. 10 ), directed into the body of the housing  4 . The flexible legs  64  extending from the mounting platen  6  are permanently fixed at their housing end to the housing  4 , i.e. they are not removable in use by the operator. They are attached to the housing  4  by means of clamping flanges  66  of the housing  4 . The flexible legs  64  are attached at their mounting platen end to the mounting platen  6  by passing through apertures in hollow projecting portions  68  that extend in the direction of the flexible legs  64  from the upper surface of the mounting platen  6 . The flexible legs  64  are provided at their mounting platen  6  end 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 to  FIG. 11 .  
         [0053]     The mounting platen  6  surrounds the second drive shaft  62 , and is spaced radially therefrom. This means that the mounting platen  6  itself is not directly driven by either of the drive shafts.  
         [0054]     In  FIG. 10 a  first sanding platen, which is a random orbit sanding head  8 , is secured next to the mounting platen  6  onto the drive shaft  62 . Securement of the random orbit sanding head  8  is achieved by a bolt  70  and washer  72 . The bolt  70  passes through an aperture in the sanding head  8 , through aperture  74  in the mounting platen (see  FIGS. 12 and 13 ), and over the driving spindle of the second drive shaft  62 . The sanding platen  8  is located in a parallel plane to the mounting platen  6 , but is spaced from it, so that there is no contact between the facing surfaces of the mounting platen  6  and the sanding shoe  8 . Therefore free rotation of the sanding platen  8  is permitted about the bearing axis  60 , and the platen  8  exhibits a random orbit.  
         [0055]     A brake pad  76  is provided on the under-surface of the mounting platen  6 . The brake pad  76  comprises a resilient member  78  in the form of a ring formed from a synthetic rubber resilient material, and an abrasion resistant contact layer  80  comprising polytetrafluoroethylene (PTFE) filed with carbon fibre or glass for increased abrasion resistance. The arrangement of the layers is such that when the sanding platen  8  is secured in place onto the drive  62  then the resilient ring  78  is under compression so that a resultant load is put by the filled PTFE layer  80  onto a reaction surface part  82  of the underlying upper surface of the sanding platen  8 . The purpose of this brake  76  is 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 shaft  50  is typically driven at a rotational speed of 12000 rpm, which is too fast a speed for rotation of the sanding platen  8 . The brake pad  76  limits the rotational speed of the platen to an acceptable operating speed, typically around 1200 rpm, or 10% of the rotational speed of the motor.  
         [0056]      FIG. 11  shows the drive unit of the hand tool with an orbital sanding platen  84  mounted in place of the random orbit platen of  FIG. 10 . Also  FIGS. 12 and 13  are perspective views of the mounting platen  8  (which is common to both  FIGS. 10 and 11 ) and the sanding platen  84  (which is shown in  FIG. 11 , but not in  FIG. 10 ).  
         [0057]      FIGS. 12 and 13  show in more detail features of the mounting platen  8 , which remains on the housing when the platens  84  and  8  are interchanged. From these Figures it can be seen that the mounting platen  8  is generally a blunt shoe shape, and is substantially flat, with a peripheral lip  86  extending downwards towards the sanding shoe  84 . The large central aperture  74 , allowing it to be positioned around the second drive shaft, radially distant therefrom, so there is no direct contact between the mounting platen  6  and the second drive shaft  62 , can also be clearly seen in these Figures, as can the four hollow right cylindrical portions  88 , integrally formed with the surface of the mounting platen  8 , and projecting into the body of the housing  4  i.e. upwards as shown in the Figures. An inner lip  90  extends downwards around most of the central aperture  74 , and joins to the outer peripheral lip  92  of the mounting platen  6  at two points  94  on one short side of the mounting platen  8 .  
         [0058]     In line with the upwardly directed projections  88 , and projecting in the other direction, from the opposite surface of the mounting platen  6  are four hollow, generally cylindrical pin shaped coupling members  96 . The pin-shaped coupling members  96  are also integrally formed with the mounting platen  8 . The substantially flat mounting platen with its projecting portions  88  and  96  are preferably integrally injection moulded from polymeric material or diecast zinc.  
         [0059]     The four coupling pins  96 , provided on the opposite surface of the mounting platen  6  from the flexible legs  64 , in corresponding positions, i.e. vertically aligned with the legs  64  as shown in  FIGS. 12 and 13  have a dual function; the pins  96  secure the legs  64  in place, and couple with an orbital sanding head  84 , in use, to prevent free rotation of that sanding head (FIGS.  11  to  13 ).  
         [0060]     Each coupling pin  96  is an integrally formed part shaped as a hollow cylinder. The pin member  96  contains a radially directed flange  98  extending partially into the hollow of the pin member  96 , to act as a stop member for a separate externally screw threaded headed bolt member  100  (see  FIGS. 10 and 11 ). The externally screw threaded bolt member  100  passes through the hollow central pin member  96 , and is shaped and sized to slide into the hollow pin member until its head abuts the internal stop flange  98 , and then screw into inner hollow screw threaded cylindrical recesses at the mounting platen end of the flexible legs  64 . By this screw threaded bolt member  100  the flexible legs  64  are therefore secured to the mounting platen.  
         [0061]     As best seen in  FIG. 11 , each pin member  96  is located between part of the peripheral lip  86  and the inner lip  90  of the mounting platen  6 . The pin member  96  of the coupling means acts to couple to the orbital sanding shoe  84  to prevent its free rotation.  
         [0062]     As shown in  FIG. 11 , when mounted on the drive unit, the orbital sanding shoe  84  is secured to the spindle of second drive shaft  62  by means of the same nut  70  and washer  72  used to secure the random orbit sanding platen  8  of  FIG. 10 . The orbital sanding shoe  84  is substantially flat, and is provided, on its upper major surface in the orientation shown in the Figure, with coupling means  92  shaped to co-operate with the coupling means  96  of the mounting platen  6 . The coupling means  92  each comprise a hollow right-cylindrical stub, projecting upwards from the surface of the sanding shoe  84 . The hollow right cylindrical projection  92  is shaped so that it provides a recess into which the pin member  96  of the mounting platen fits. One side of the cylindrical projection  92  on the sanding shoe  84  fits between the peripheral lip  86  of the mounting platen  6  and the outer surface of the pin member  96  of the mounting platen  6 ; and the opposite side of the cylindrical projection  92  on the sanding shoe  84  fits between the inner lip  90  of the mounting platen  6  and the opposite outer surface of the pin member  96  of the mounting platen  6 .  
         [0063]     By means of the co-operating coupling means  96  and  92 , the sanding shoe  84  and mounting platen  6  are therefore securely located substantially to prevent relative movement between the mounting platen  6  and the sanding shoe  84  in a plane perpendicular to the axis of the bearing  60 . Relative movement parallel to the axis of the bearing  60  is, of course, prevented by the nut  70  and washer  72  attachment.  
         [0064]     In operation, when the motor is switched on and the drive shafts  50  and  62  turn, since the sanding shoe  84  is prevented from rotation relative to the mounting platen  6 , and the mounting platen  6  is fixed relative to the housing  4  by means of legs  64 , then free rotation of the sanding shoe  84  around the bearing  60  axis is prevented. The flexibility in the legs  64 , however, allows the sanding platen  84  to follow the rotating motion of the eccentric spindle itself driven by the first drive shaft  50 . Therefore the sanding shoe  84  is allowed to oscillate within a fixed orbit due to the flexibility of the legs  64 .  
         [0065]     In order to ensure that the sanding shoe  84  is always located the correct way round on the mounting platen  6 , the coupling means  96  and  92  are non uniformly spaced over the surface of the mounting platen  6  and the sanding platen  84 , those on one lateral side of the platens (the right as shown in  FIGS. 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).  
         [0066]     It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.

Technology Classification (CPC): 1