U.S. patent application number 10/902750 was filed with the patent office on 2005-11-24 for mode selection mechanism for power tool, and power tool incorporating such mechanism.
Invention is credited to Walker, Andrew.
Application Number | 20050257385 10/902750 |
Document ID | / |
Family ID | 34930320 |
Filed Date | 2005-11-24 |
United States Patent
Application |
20050257385 |
Kind Code |
A1 |
Walker, Andrew |
November 24, 2005 |
Mode selection mechanism for power tool, and power tool
incorporating such mechanism
Abstract
A mode selection apparatus for a jigsaw having scrolling and
orbital modes is disclosed. The mode selection apparatus comprises
a locking arm (76) moveable between a first position in which a
scroller knob (56) is rotatable relative to the tool housing, a
second position in which the locking arm engages the scroller knob
to prevent it from rotating relative to the tool housing and an
output shaft of the jigsaw is prevented from pivoting about a pivot
axis transverse to the longitudinal axis of the output shaft, and a
third position in which the scroller knob is prevented from
rotating relative to the tool housing and the output shaft is
causes to pivot about the pivot axis. The locking arm (76) has a
slot (84) for engaging a tooth (86) on a scroll selector (48) for
moving the locking arm between the first, second and third
positions thereof. The tooth (86) remains in engagement with the
slot (84) during movement of the locking arm between the first,
second and third positions.
Inventors: |
Walker, Andrew; (Newton
Hall, GB) |
Correspondence
Address: |
Bruce S. Shapiro
Black & Decker Corporation
Mail Stop TW199
701 E. Joppa Rd
Towson
MD
21286
US
|
Family ID: |
34930320 |
Appl. No.: |
10/902750 |
Filed: |
July 29, 2004 |
Current U.S.
Class: |
30/392 |
Current CPC
Class: |
B23D 49/16 20130101;
B23D 49/165 20130101; B23D 49/167 20130101 |
Class at
Publication: |
030/392 |
International
Class: |
E21B 003/00; E21B
017/22 |
Foreign Application Data
Date |
Code |
Application Number |
May 18, 2004 |
EP |
EP 04252931.3 |
Claims
1. A mode selection apparatus for a power tool having a tool
housing, a motor arranged in the tool housing, and an output shaft
adapted to be driven in a reciprocating motion relative to the tool
housing by means of the motor and to support a working member of
the tool for reciprocating motion of the working member relative to
the tool housing, the mode selection apparatus comprising: at least
one locking member moveable between a respective first position in
which said output shaft of the tool is pivotable about its
longitudinal axis, a respective second position in which the output
shaft is prevented from pivoting about its longitudinal axis and is
prevented from engaging a drive mechanism to prevent the output
shaft from pivoting about a pivot axis transverse to said
longitudinal axis, and a respective third position in which the
output shaft is prevented from pivoting about its longitudinal axis
and engages said drive mechanism to cause the output shaft to pivot
about the pivot axis transverse to said longitudinal axis, wherein
said locking member has at least one respective recess; and at
least one mode selection member for engaging said locking member
for moving the locking member between first, second and third
positions thereof and having at least one protrusion for engaging
said recess on said locking member; wherein at least one said
protrusion of said mode selection member is adapted to remain in
engagement with the corresponding said recess of said locking
member during movement of said locking member between said first,
second and third positions thereof.
2. An apparatus according to claim 1, wherein at least one said
locking member is adapted to engage a first actuator member on said
tool housing in said second and third positions to prevent rotation
of said first actuator member relative to the tool housing.
3. An apparatus according to claim 2, wherein at least one said
locking member is adapted to engage at least one respective slot on
the first actuator member.
4. An apparatus according to claim 1, wherein at least one said
mode selection member has at least one respective cam surface for
causing the output shaft to move out of engagement with the drive
mechanism to prevent the output shaft from pivoting about the pivot
axis transverse to said longitudinal axis.
5. An apparatus according to claim 4, wherein at least said one cam
surface is a groove.
6. An apparatus according to claim 5, wherein at least one said cam
surface is a protrusion.
7. An apparatus according to claim 1, wherein at least one said
mode selection member is adapted to rotate relative to the tool
housing.
8. An apparatus according to claim 1, further comprising at least
one first actuator member for enabling rotation of the output shaft
about said longitudinal axis.
9. An apparatus according to claim 8, further comprising at least
one second actuator member for actuating at least one said mode
selection member for moving at least one said locking member
between first, second and third positions thereof.
10. An apparatus according to claim 1, said power tool comprising a
jigsaw.
11. A jigsaw comprising: a housing; a motor; an output shaft driven
in reciprocating motion relative to the tool housing by said motor
and supporting a working member, said output shaft disposed for
both rotational motion about a longitudinal axis thereof and
pivoting motion about an axis transverse to said longitudinal axis;
a cam face and a cam follower operatively disposed between said
motor and said output shaft and selectively disposed so as to
cooperate to drive said output shaft in said pivoting motion; a
locking arm movable in the direction of said longitudinal axis
between a first position in which said output shaft is rotable
about its longitudinal axis and said cam face and said cam follower
are displaced from each other such that said output shaft is not
driven in pivoting motion, a second position in which the output
shaft is prevented from rotating about its longitudinal axis and
said cam face and said cam follower are displaced from each other
such that said output shaft is not driven in pivoting motion, and a
third position in which the output shaft is prevented from rotating
about its longitudinal axis and said cam face and said cam follower
cooperate to drive said output shaft in pivoting motion.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a mode selection mechanism
for a power tool, and relates particularly, but not exclusively, to
a mode selection mechanism for preventing simultaneous actuation of
a scrolling mode of a jigsaw (i.e. in which an output shaft
supporting a jigsaw blade can rotate about its longitudinal axis
relative to the jigsaw housing) and an orbital mode of a jigsaw
(i.e. in which the output shaft is pivotable relative to the
housing about an axis transverse to its longitudinal axis, so that
an oscillating motion is superimposed on the axial reciprocating
motion of the jigsaw blade). The invention also relates to a power
tool incorporating such a mode selection mechanism.
BACKGROUND OF THE INVENTION
[0002] EP0158325 discloses a jigsaw having (i) a scrolling mode in
which an output shaft and jigsaw blade can rotate about a
longitudinal axis of the output shaft to enable cutting of smaller
radii of curvature or more intricate types of cut than conventional
jigsaws in which the jigsaw blade only faces forwards, and (ii) an
orbital mode in which the output shaft oscillates about a pivot in
a fore and aft direction to assist the cutting action of the jigsaw
blade.
[0003] In jigsaws having a scrolling mode and an orbital mode, it
is desirable to prevent simultaneous actuation of the scrolling and
orbital modes, since the jigsaw is difficult to operate when in the
orbital mode when the jigsaw blade is not oriented forwards
relative to the jigsaw housing. In the jigsaw of EP0158325, this is
carried out by means of a mode selection mechanism in which a mode
selector is provided with a pinion and a cam surface, such that in
an orbital mode, the pinion moves a rack into engagement with a
scroller knob to prevent rotation of the scroller knob relative to
the housing, while in the scrolling mode, the cam surface prevents
pivoting movement of the output shaft of the jigsaw about its
pendulum axis. However, this known arrangement suffers from the
drawback that the rack and pinion mechanism is of complicated
construction and relatively difficult to assemble, which
significantly increases the cost of production of a jigsaw
incorporating this mechanism.
[0004] Another jigsaw having scrolling and orbital modes is
disclosed in DEU8702727.5. In this jigsaw, a mode selection knob
moves a carriage between an upper position in the orbital mode, in
which rotation of an output shaft of the jigsaw about its
longitudinal axis is prevented, and a lower position in the
scrolling mode, in which pivoting of the output shaft about an axis
transverse to its longitudinal axis is prevented. However, this
jigsaw suffers from the disadvantage that the carriage cannot be
used to simultaneously disable the scrolling and orbital modes, as
a result of which a further actuator mechanism is required. This in
turn has the disadvantage of increasing the cost of production of
the jigsaw and making the jigsaw less easy to use.
[0005] Preferred embodiments of the present invention seek to
overcome the above disadvantages of the prior art.
BRIEF SUMMARY OF THE INVENTION
[0006] According to an aspect of the present invention, there is
provided a mode selection apparatus for a power tool having a tool
housing, a motor arranged in the tool housing, and an output shaft
adapted to be driven in a reciprocating motion relative to the tool
housing by means of the motor and to support a working member of
the tool for reciprocating motion of the working member relative to
the tool housing, the mode selection apparatus comprising:
[0007] at least one locking member moveable between a respective
first position in which an output shaft of the tool is pivotable
about its longitudinal axis, a respective second position in which
the output shaft is prevented from pivoting about its longitudinal
axis and is prevented from engaging a drive mechanism to prevent
the output shaft from pivoting about a pivot axis transverse to
said longitudinal axis, and a respective third position in which
the output shaft is prevented from pivoting about its longitudinal
axis and engages said drive mechanism to cause the output shaft to
pivot about the pivot axis transverse to said longitudinal axis,
wherein said locking member has at least one respective first
protrusion and/or recess; and
[0008] at least one mode selection member for engaging a respective
said locking member for moving the locking member between first,
second and third positions thereof and having at least one second
protrusion and/or recess for engaging a respective said first
recess and/or protrusion on said locking member;
[0009] wherein at least one said protrusion and/or recess of a said
mode selection member is adapted to remain in engagement with the
corresponding said recess and/or protrusion of a said locking
member during movement of said locking member between said first,
second and third positions thereof.
[0010] By providing at least one protrusion and/or recess of a mode
selection member which is adapted to remain in engagement with the
corresponding recess and/or protrusion of a locking member during
movement of the locking member between its first, second and third
positions, this provides the advantage of making the mode selection
apparatus of more simple construction and easier to assemble than a
mechanism employing a rack and pinion, which significantly reduces
the cost of production of a tool incorporating the apparatus. In
addition, by providing at least one mode selection member for
moving a respective locking member between the first, second and
third positions thereof, this provides the advantage of enabling
three modes of a tool incorporating the mode selection apparatus,
for example scrolling mode, orbital mode and conventional mode of a
jigsaw, to be selected by means of a single actuator, which in turn
makes the tool more convenient to operate.
[0011] At least one said locking member may be adapted to engage a
first actuator member on said tool housing in said first and second
positions to prevent rotation of said first actuator member
relative to the tool housing.
[0012] At least one said locking member may be adapted to engage at
least one respective slot and/or protrusion on the first actuator
member.
[0013] At least one said mode selection member may have at least
one respective cam surface for causing the output shaft to move out
of engagement with the drive mechanism to prevent the output shaft
from pivoting about the pivot axis transverse to said longitudinal
axis.
[0014] At least said one cam surface may be a groove.
[0015] At least one said cam surface may be a protrusion.
[0016] At least one said mode selection member may be adapted to
rotate relative to the tool housing.
[0017] The apparatus may further comprise at least one first
actuator member for enabling rotation of the output shaft about
said longitudinal axis.
[0018] The apparatus may further comprise at least one second
actuator member for actuating at least one said mode selection
member for moving at least one said locking member between first,
second and third positions thereof.
[0019] According to another aspect of the present invention, there
is provided a power tool having a tool housing, a motor arranged in
the tool housing, an output shaft adapted to be driven in a
reciprocating motion relative to the tool housing by means of the
motor and to support a working member of the tool for reciprocating
motion of the working member relative to the tool housing, and a
mode selection apparatus as defined above.
[0020] The power tool may be a jigsaw.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] 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:
[0022] FIG. 1 is a cross-sectional elevation view of a jigsaw
embodying the present invention;
[0023] FIG. 2 is a perspective view of a blade support assembly,
jigsaw blade and scrolling knob of the jigsaw of FIG. 1;
[0024] FIG. 3 (a) is a perspective view of an upper bearing of the
blade support assembly of FIG. 2;
[0025] FIG. 3(b) is a front view of the upper bearing of FIG.
3(a);
[0026] FIG. 3(c) is a top view of the upper bearing of FIG.
3(a);
[0027] FIG. 3(d) is a side view of the upper bearing of FIG.
3(a);
[0028] FIG. 3(e) is a bottom view of the upper bearing of FIG.
3(a);
[0029] FIG. 3(f) is a side cross sectional view of the upper
bearing of FIG. 3(a);
[0030] FIG. 4 is a side view of the blade support assembly, jigsaw
blade and scrolling knob of FIG. 2, together with a drive mechanism
of the jigsaw of FIG. 1, but having an alternative embodiment of
scroll selector to the arrangement shown in FIG. 1;
[0031] FIG. 5(a) is a perspective view of the scroller knob and
scroller locking mechanism of FIG. 4 in a scrolling mode of the
jigsaw;
[0032] FIG. 5(b) is a perspective view, corresponding to FIG. 5(a)
of the scroller knob and scroller locking mechanism in a
conventional mode of the jigsaw;
[0033] FIG. 5(c) is a perspective view, corresponding to FIG. 5(a)
of the scroller knob and scroller locking mechanism in an orbital
mode of the jigsaw;
[0034] FIG. 6(a) is a front view of a scotch yoke, output shaft and
blade clamp of the blade support assembly of FIG. 2;
[0035] FIG. 6(b) is a perspective view of the scotch yoke, output
shaft and blade clamp of FIG. 6(a);
[0036] FIG. 6(c) is a top view of the scotch yoke of FIGS. 6(a) and
6(b);
[0037] FIG. 7 is a perspective view of the blade support assembly
of FIG. 2;
[0038] FIG. 8 is a top view of the blade support assembly of FIG.
7;
[0039] FIG. 9 is a rear view of the blade support assembly of FIG.
7;
[0040] FIG. 10 is a side cross sectional view along the line A-A in
FIG. 8;
[0041] FIG. 11 is a view along the line B-B in FIG. 10;
[0042] FIG. 12 is an enlarged view of the lower part of the blade
support assembly of FIG. 10 when the blade is not cutting a
workpiece; and
[0043] FIG. 13 is a view corresponding to FIG. 12 when the blade is
cutting a workpiece.
DETAILED DESCRIPTION OF THE INVENTION
[0044] Referring to FIG. 1, a jigsaw 2 has a housing 4 comprising
two clam shell halves 6 (only one of which is shown in FIG. 1)
defining a handle 8 having a trigger switch 10 for operating a
motor 12 supplied with electrical power via a cable 14. A shoe 16
for resting on a workpiece (not shown) is located at a lower part
of the housing 4, and a jigsaw blade 18 (FIG. 2) is attached to the
lower end of an output shaft 20 by means of a blade clamp mechanism
22. The operation of the blade clamp mechanism 22 is not relevant
to an understanding of the present invention and will therefore not
be described in greater detail herein. The orientation of the shoe
16 is adjustable relative to the housing 4 to enable bevel cutting,
and can be fixed by means of a clamping screw 24 operated by a
locking mechanism 26, which is also not relevant to an
understanding of the present invention and will therefore not be
described in greater detail.
[0045] The motor 12 drives a shaft 28 which carries a fan 30. When
the fan 30 rotates, air is expelled via duct 32 and may be used to
blow sawdust away from the vicinity of blade 18, and draws air
through inlets 34 in housing 4 to cool motor 12. The shaft 28
carries a pinion 36 which meshes with a drive gear 38 mounted about
axis 40, the gear 38 carrying a cam surface 42 on its front face. A
cam follower 44 is selectively engageable with cam surface 42 by
means of cam portion 46 of scroll selector 48 to operate an orbital
mode of the jigsaw in a manner which will be described in greater
detail below. The gear 38 also carries an eccentric pin 50 which
slidably fits in a slot 52 of scotch yoke mechanism 54 mounted to
output shaft 20.
[0046] Referring now to FIG. 2, a scroller knob 56 is rotatably
mounted to the housing 4 for adjusting the orientation of the blade
18 relative to the housing 4. The scroller knob 56 has a collar
portion 58 having a cruciform bore 60 therein, the purpose of which
is described in greater detail below. A blade support assembly 62
has a support housing 64 having trunnions 66 which are received in
corresponding recesses (not shown) in housing 4 to enable the
assembly 62 to pivot about axis X-X relative to the housing 4 in
the orbital mode of the jigsaw. An upper bearing 68 (FIG. 3) has a
partially spherical portion 70 which is rotatable about axis Y-Y
relative to support housing 64, and has a slot 72 therethrough for
receiving the output shaft 20 such that the output shaft 20 can
slide in the direction of axis Y-Y relative to the upper bearing
68, but is prevented from moving relative to the bearing 68 in a
direction transverse to the axis Y-Y. The upper bearing 68 also has
a pair of legs 74 which are received in cruciform bore 60 of
scroller knob 56 such that the bearing 68 (and therefore the output
shaft 20) rotates with the scroller knob 56 about axis Y-Y, but
limited pivoting movement of the bearing 68 about axis X-X relative
to the scroller knob 56 is permitted.
[0047] A mechanism for selecting between the scrolling, orbital and
conventional modes of the jigsaw is shown in detail with reference
to FIGS. 4 and 5. A locking arm 76 is slidably mounted to the
housing 4 and is moveable between a lower position, as shown in
FIG. 5(a) in which the scroller knob 56 can rotate relative to the
housing 4, and two upper positions shown in FIGS. 5(b) and 5(c) in
which an upper end 78 of the locking arm 76 is received in one or
more slots 80 in the underside of scroller knob 56 to prevent
rotation of the scroller knob 56 about axis Y-Y relative to the
housing 4. The scroll selector 48 is rotatably mounted to the
housing 4 and can be rotated by means of a mode selector knob (not
shown) on the housing 4, and a lower end 82 of locking arm 76 has a
rounded slot 84 which receives a rounded tooth 86 provided on
scroll selector 48 such that rotation of scroll selector 48
relative to the housing 4 causes movement of the locking arm 76
parallel to the axis Y-Y. The scroll selector 48 also carries a cam
surface, which is a protrusion 46 in the embodiment of FIG. 1 and a
groove 88 in the embodiment of FIGS. 5(a) to 5(c).
[0048] Referring now to FIGS. 5(a) to 5(c), in the position shown
in FIG. 5(a), the rotational position of scroll selector 48 about
axis 90 relative to the housing 4 is such that the upper end 78 of
locking arm 76 is not receiving in any of the grooves 80 in
scroller knob 56, as a result of which the scroller knob 56 (and
therefore also the output shaft 20 and jigsaw blade 18) can rotate
about axis Y-Y relative to the housing 4 to permit scrolling motion
of the blade 18. At the same time, it is desirable to prevent
orbital motion of the blade 18 when the jigsaw is in the scroller
mode, since it is difficult to operate the jigsaw in the orbital
mode when the orientation of the blade 18 relative to the housing 4
is not forwards. This is achieved in the position shown in FIG.
5(a) because the lower part 82 of locking arm 76 is not received
within recess 88, as a result of which the locking arm 76 is urged
forwards relative to the scroll selector 48. This in turn abuts
lower portion 92 (FIG. 2) of support housing 64, which causes the
support assembly 62 to pivot forwards against the action of a
spring (not shown) about axis X-X so that cam follower 44 is held
out of engagement with cam face 42 on gear 38. As a result,
pendulum motion cannot be imparted to the support assembly 62 as
the gear 38 rotates.
[0049] As the scroll selector 48 is rotated anticlockwise about
axis 90 to the position shown in FIG. 5(b), engagement of tooth 86
with slot 84 causes the locking arm 76 to move upwards so that its
upper end 78 is received in a slot 80 in scrolling knob 56 to
prevent rotation of the scrolling knob 56 relative to the housing
4. At the same time, the lower end 82 of the locking arm 76 is
still not received in recess 88, as a result of which the cam
follower 44 is still held out of engagement with the cam surface 42
on gear 38, so pendulum action cannot be imparted to the support
assembly 62.
[0050] As the scroll selector 48 is further rotates anticlockwise
about axis 90 to the position shown in FIG. 5(c), the upper end 78
of locking arm 76 is received further in groove 80, but the lower
end 82 of locking arm 76 is now received in recess 88 on scroll
selector 48. As a result, the support assembly 62 and locking arm
76 can pivot under the action of the spring (not shown) to bring
the cam follower 44 into engagement with cam surface 42 on gear 38,
so that pendulum action is imparted to the support assembly 62 as
the gear 38 is rotated by motor 12. It can therefore be seen that
the scrolling mode is not permitted when the orbital mode is
active, and vice versa. By operating the locking arm 76 by means of
the engagement of a tooth 86 in a groove 84 (as opposed to
cooperating rack and pinion), this provides the advantage of
significantly simplifying manufacture and assembly of the scroll
locking mechanism, which in turn reduces the cost of production of
the jigsaw.
[0051] Referring now to FIGS. 6(a) to 6(c), the output shaft 20 is
of rectangular cross section along most of its length. This
provides the advantage that the ends of the shaft 20 can be
non-rotatably mounted to adjacent parts without the need to provide
cross pins (which would be necessary in the case of a shaft of
circular cross section) through the shaft which would need to fit
into slots at least as deep as the distance of travel of the cross
pins during reciprocating motion of the shaft 20. As a result, the
parts of the jigsaw at the ends of the shaft 20 can be made of
significantly more compact construction than is the case with a
shaft of circular cross section.
[0052] In order to enable rotation of the shaft 20 relative to the
scotch yoke 54 in scrolling mode of the jigsaw, a pair of generally
D-shaped inserts 94 are mounted on opposite sides of the shaft 20
to provide that part of the shaft with a partially circular
external cross section, and the scotch yoke 54 is rotatably mounted
to the shaft 20 by means of circular apertures 96 in upper and
lower flanges 98 of the scotch yoke 54. The scotch yoke 54 is then
fixed to the shaft 20 by means of pins 100 through D-shaped inserts
94 and shaft 20 so that the scotch yoke 54 cannot move axially
relative to the shaft 20, but can pivot about relative to the shaft
so that the slot 52 of scotch yoke 54 continues to face eccentric
pin 50 (FIG. 1) regardless of the orientation of the blade 18
relative to the housing 4. This enables the blade 18 to be driven
in a reciprocating manner when the jigsaw is in the scroller
mode.
[0053] The support assembly 62 of FIG. 2 is shown in detail in
FIGS. 7 to 13. A lower bearing 102 is rotatably mounted about the
longitudinal axis of the output shaft 20 to the support housing 64
and has a slot, similar to the slot 72 in upper bearing 68, for
slidably receiving the shaft 20 so that the shaft can execute
reciprocating axial movement relative to the bearings 68, 102, but
is prevented from moving in a direction transverse to its
longitudinal axis. The lower bearing 102 has four protruding legs
104 at its lower end, so that a cruciform slot (FIG. 11) is defined
between the legs 104 for receiving the shaft 20 and for cooperating
with ribs 120 provided on a control bearing 106 such that the
control bearing 106 rotates with the lower bearing 102 and output
shaft 20 as the output shaft rotates about its longitudinal axis.
The control bearing 106 is rotatably mounted to support housing 64
by means of engagement of a flange 116 on support housing 64 with a
groove in control bearing 106.
[0054] The control bearing 106 has a support arm 108 which carries
a blade support roller 110 at a distal end thereof. The blade
support roller 110 has a groove 112 (FIG. 1) for receiving the rear
face of jigsaw blade 18. Because the control bearing 106 is
rotatably mounted to support housing 64, the blade support roller
110 remains in contact with the jigsaw blade 18 in the scrolling,
orbital and conventional modes of the jigsaw. The lower bearing
102, control bearing 106 and support housing 64 are so dimensioned
that limited pivoting of control bearing 106 relative to lower
bearing 102 is possible about an axis transverse to the
longitudinal axis of the shaft 20, and limited movement of the
control bearing 106 relative to the support housing 64 is possible,
with movement due to clearance 122 between control bearing 106 and
support housing 64 being taken up by an elastomeric seal 118, which
also prevents leakage of lubricant from the interior of the support
assembly 62.
[0055] Referring now in detail to FIGS. 12 and 13, when the jigsaw
is used to cut a workpiece (not shown), the reaction force from the
workpiece acting on the blade 18 tends to cause the blade 18 to
pivot clockwise relative to the shaft 20 form the position shown in
FIG. 12 to that shown in FIG. 13. As a result, a turning moment is
applied via blade support roller 110 to the support arm 108 in the
direction of arrow C shown in FIG. 13. This turning moment is
opposed by an opposite turning moment applied to the control
bearing 106 by the support housing 64 as the clearance 122 is
reduced from the arrangement shown in FIG. 12c to that shown in
FIG. 13.
[0056] However, as a result if the limited pivoting movement
permitted between control bearing 106 and lower bearing 102, the
turning moment applied by the support arm 108 to the support
housing 64 is not transferred to the lower bearing 102, and is
therefore not transferred to the shaft 20. The therefore provides
the advantage that frictional forces between the lower bearing 102
and shaft 20 are not increased as a result if reaction force F
(FIG. 13) acting on blade support roller 110.
[0057] 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.
* * * * *