FIELD OF THE INVENTION AND PRIOR ART
[0001] The present invention relates to a telescopic boom according to the preamble of claim
1.
[0002] Telescopically extendable and retractable booms are frequently used for instance
on different types of cranes and are known in various configurations. In a telescopic
boom having two or more displaceable boom sections, every displaceable boom section
may be provided with its own hydraulic cylinder in order to control the extension
and retraction of the boom section. It is also known to use a hydraulic cylinder for
displacing a first displaceable boom section in relation to a fixed support or fixed
boom section and a flexible transmission member, e.g. in the form of a belt or chain,
for displacing a second displaceable boom section in relation to the first displaceable
boom section, as disclosed in
US 4 193 505 A and
FR 2 708 584 A1.
SUMMARY OF THE INVENTION
[0003] The object of the present invention is to provide a telescopic boom of new and advantageous
design.
[0004] According to the invention, this object is achieved by a telescopic boom having the
features defined in claim 1.
[0005] The telescopic boom of the present invention comprises:
- a first boom section;
- a second boom section mounted to the first boom section so as to be axially displaceable
in relation to the first boom section;
- a third boom section mounted to the second boom section so as to be axially displaceable
in relation to the second boom section;
- an actuating member acting on the second boom section for displacing the second boom
section axially in relation to the first boom section;
- an elongated, flexible first transmission member, which is arranged inside the boom
sections and has a first point fixed in relation to the first boom section and a second
point fixed in relation to the third boom section; and
- an elongated, flexible second transmission member, which is arranged inside the boom
sections and has a first point fixed in relation to the first boom section and a second
point fixed in relation to the third boom section.
The first transmission member extends inside the boom sections between its first and
second points over a first pulley, which is fixed in axial position in relation to
the second boom section, the first pulley being arranged to act on the first transmission
member so as to displace said second point of the first transmission member and thereby
the third boom section axially outwards in relation to the second boom section when
the second boom section is displaced axially outwards in relation to the first boom
section under the effect of the actuating member.
The second transmission member extends inside the boom sections between its first
and second points over a second pulley, which is fixed in axial position in relation
to the second boom section, the second pulley being arranged to act on the second
transmission member so as to displace said second point of the second transmission
member and thereby the third boom section axially inwards in relation to the second
boom section when the second boom section is displaced axially inwards in relation
to the first boom section under the effect of the actuating member.
[0006] Thus, the transmission members and the pulleys will force the third boom section
to move axially in relation to the second boom section when the second boom section
is moved axially in relation to the first boom section and will thereby cause a synchronization
of the axial movements of the individual boom sections when the boom is extended and
retracted. With the solution according to the invention, the transmission members
extend only inside the boom sections and do no pass through any area between two adjacent
boom sections. Thus, the transmission members and their pulleys are all located inside
the boom sections and are thereby well protected against weather influences and dirt
and protected against collisions with outside elements. A further advantage with this
internal location of the transmission members and their pulleys is that no parts other
than sliding elements need to be located in the areas between the boom sections. Hereby,
the dimensions of the sliding elements can be optimized to reduce normal stress on
the boom sections.
[0007] According to an embodiment of the invention, the first pulley and the second pulley
are mounted to an elongated support unit, which is fixed to the second boom section
at the inner end thereof and extends axially inside the second and third boom sections,
the first pulley being mounted at the outer end of the support unit and the second
pulley being mounted at the inner end of the support unit. Hereby, the pulleys can
be mounted inside the boom sections in a simple manner.
[0008] Another embodiment is
characterized in:
- that the boom comprises an elongated, flexible third transmission member extending in
parallel to the second transmission member;
- that the third transmission member is arranged inside the boom sections and has a
first point fixed in relation to the first boom section and a second point fixed in
relation to the third boom section;
- that the third transmission member extends inside the boom sections between its first
and second points over a third pulley, which is fixed in axial position in relation
to the second boom section, the third pulley being arranged to act on the third transmission
member so as to displace said second point of the third transmission member and thereby
the third boom section axially inwards in relation to the second boom section when
the second boom section is displaced axially inwards in relation to the first boom
section under the effect of the actuating member;
- that the second pulley and the third pulley are mutually concentric and mounted to
the support unit on opposite sides thereof symmetrically in relation to the centre
axis of the support unit; and
- that the first pulley is mounted in a plane which extends through the centre axis
of the support unit and forms the plane of symmetry for the second and third pulleys.
Hereby, the forces acting on the support unit in connection with mutual displacements
of the boom sections will be well balanced.
[0009] According to another embodiment of the invention, the actuating member comprises:
- a cylinder part, which is fixed in axial position in relation to the second boom section
and which constitutes a body part of the support unit,
- a piston, which is mounted inside the cylinder part so as to be axially displaceable
in relation to the cylinder part, and
- a piston rod, which is secured to the piston and fixed in axial position in relation
to the first boom section.
In this case, the cylinder part functions as a vital part of the actuating member
as well as the support unit, which will make it possible to achieve a very compact
construction of these appliances and facilitate the mounting thereof inside the boom
sections.
[0010] According to another embodiment of the invention, the boom comprises at least one
flexible conduit in the form of a hose or cable, which is arranged inside the boom
sections and has a first point fixed in relation to the first boom section and a second
point fixed in relation to the third boom section, said conduit extending inside the
boom sections between its first and second points over a pulley, which is fixed in
axial position in relation to the second boom section and arranged to act on the conduit
so as to keep the conduit stretched out and prevent it from slackening when the boom
sections are axially displaced in relation to each other.
[0011] Further advantageous features of the boom according to the invention will appear
from the dependent claims and the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] With reference to the appended drawings, a specific description of preferred embodiments
of the invention cited as examples follows below. In the drawings:
- Fig 1
- is a schematic illustration of a telescopic boom according to a first embodiment of
the present invention, as seen in a cut lateral view and with the boom sections of
the boom in an extended position,
- Fig 2
- shows the boom of Fig 1 with the boom sections in a retracted position,
- Fig 3
- is a schematic illustration of a telescopic boom according to a second embodiment
of the invention, as seen in a cut lateral view and with the boom sections of the
boom in an extended position,
- Fig 4
- shows the boom of Fig 3 with the boom sections in a retracted position,
- Figs 5 and 6
- illustrate the arrangement of flexible conduits in the boom of Figs 3 and 4,
- Figs 7-11
- are perspective views illustrating different stages in a process of assembling a boom
of the type illustrated in Figs 3-6, and
- Fig 12
- is an illustration corresponding to Fig 10, with the boom sections shown in a cut
planar view from above.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0013] Telescopic booms 1, 1' according to two different embodiments of the present invention
are illustrated in Figs 1-4. In the illustrated embodiments, the respective boom 1,
1' comprises three boom sections 2, 3, 4. A first boom section 2 constitutes an innermost
base section of the boom. A second boom section 3 constitutes an intermediate section
of the boom and is mounted to the first boom section 2 so as to be axially displaceable
in relation thereto. A third boom section 4 constitutes an outermost section of the
boom and is mounted to the second boom section 3 so as to be axially displaceable
in relation thereto. The boom sections 2, 3, 4 are tubular and together they delimit
an inner space 5 of the boom. The third boom section 4 is slidingly received in the
second boom section 3, which in its turn is slidingly received in the first boom section
2. The boom 1, 1' is telescopically extendable by displacement of the second and third
boom sections 3, 4 outwards in relation to the first boom section 2 and telescopically
retractable by displacement of the second and third boom sections 3, 4 inwards in
relation to the first boom section 2.
[0014] The boom sections 2, 3, 4 are in a conventional manner provided with sliding elements
8 so as to allow the third boom section 4 to be slidingly supported against the second
boom section 3 and the second boom section 3 to be slidingly supported against the
first boom section 2, as illustrated in Figs 1-4.
[0015] The boom 1, 1' comprises an actuating member 6 acting on the second boom section
3 for displacing the second boom section 3 axially in relation to the first boom section
2. The actuating member 6 is with advantage a hydraulic cylinder comprising a cylinder
part 6a, a piston (not shown) mounted inside the cylinder part 6a so as to be axially
displaceable in relation to the cylinder part, and a piston rod 6b secured to the
piston. However, any other suitable type of actuating member capable of displacing
the second boom section 3 axially in relation to the first boom section 2 could be
used.
[0016] In the embodiment illustrated in Figs 1 and 2, the actuating member 6 is a hydraulic
cylinder with the cylinder part 6a fixed in axial position in relation to the first
boom section 2 and with the piston rod 6b fixed in axial position in relation to the
second boom section 3. The piston rod 6b could alternatively by fixed in axial position
in relation to the first boom section 2 and the cylinder part 6a fixed in axial position
in relation to the second boom section 3, if so desired. In the example illustrated
in Figs 1 and 2, the actuating member 6 is mounted on the outside of the first and
second boom sections 2, 3, but it could alternatively be mounted inside the boom sections
in the above-mentioned inner space 5.
[0017] In the embodiment illustrated in Figs 3-12, the actuating member 6 is a hydraulic
cylinder mounted in the inner space 5 of the boom sections with the cylinder part
6a fixed in axial position in relation to the second boom section 3 and with the piston
rod 6b fixed in axial position in relation to the first boom section 2.
[0018] The boom 1, 1' comprises an elongated, flexible first transmission member 10 in the
form of a belt or cable or chain or the like, which is arranged in the inner space
5 of the boom sections. This transmission member 10 has a first point 11 fixed in
relation to the first boom section 2 and a second point 12 fixed in relation to the
third boom section 3. The transmission member 10 extends inside the boom sections
between said first and second points 11, 12 over a pulley 13, in the following denominated
first pulley, which is fixed in axial position in relation to the second boom section
3. The first pulley 13 is arranged to act on the first transmission member 10 so as
to displace said second point 12 of the first transmission member and thereby the
third boom section 4 axially outwards in relation to the second boom section 3 when
the second boom section is displaced axially outwards in relation to the first boom
section 2 under the effect of the actuating member 6. Thus, when the second boom section
3 is moved outwards by the actuating member 6, the first pulley 13 will be moved together
with the second boom section away from said first point 11 so that said second point
12 is forced to move outwards, thereby driving also the third boom section 4 outwards.
The first pulley 13 is located closer to the outer end of the boom as compared to
said first and second points 11, 12 of the first transmission member 10. Thus, the
first transmission member 10 extends forwards from the first point 11 in the direction
towards the outer end of the boom, around the first pulley 13 and then backwards from
the first pulley 13 to the second point 12 in the direction towards the inner end
of the boom.
[0019] The boom 1, 1' also comprises an elongated, flexible second transmission member 20
in the form of a belt or cable or chain or the like, which is arranged in the inner
space 5 of the boom sections. This transmission member 20 has a first point 21 fixed
in relation to the first boom section 2 and a second point 22 fixed in relation to
the third boom section 4. The transmission member 20 extends inside the boom sections
between said first and second points 21, 22 over a pulley 23, in the following denominated
second pulley, which is fixed in axial position in relation to the second boom section
3. The second pulley 23 is arranged to act on the second transmission member 20 so
as to displace said second point 22 of the second transmission member and thereby
the third boom section 4 axially inwards in relation to the second boom section 3
when the second boom section is displaced axially inwards in relation to the first
boom section 2 under the effect of the actuating member 6. Thus, when the second boom
section 3 is moved inwards by the actuating member 6, the second pulley 23 will be
moved together with the second boom section away from said first point 21 so that
said second point 22 is forced to move inwards, thereby driving also the third boom
section 4 inwards. The second pulley 23 is located closer to the inner end of the
boom as compared to said first and second points 21, 22 of the second transmission
member 20. Thus, the second transmission member 20 extends backwards from the first
point 21 in the direction towards the inner end of the boom, around the second pulley
23 and then forwards from the second pulley 23 to the second point 22 in the direction
towards the outer end of the boom. The first pulley 13 is suitably located close to
the outer end of the second boom section 3 and the second pulley 23 close to the inner
end of the second boom section.
[0020] In the illustrated embodiments, the first and second transmission members 10, 20
are designed as separate parts. However, the first and second transmission members
could alternatively constitute different sections of one and the same belt or cable
or chain or the like.
[0021] The boom 1, 1' comprises a rigid elongated element 50, for instance in the form of
a rod, which extends axially in the inner space 5 of the boom sections and is fixed
in axial position in relation to the first boom section 2. The elongated element 50
is secured to the first boom section 2 at the inner end thereof. The above-mentioned
first point 21 of the second transmission member 20 is fixed to the elongated element
50 at the outer end thereof. In the embodiment illustrated in Figs 1 and 2, also the
above-mentioned first point 11 of the first transmission member 10 is fixed to the
elongated element 50 at the outer end thereof. The first point 11 of the first transmission
member 10 may however alternatively be fixed directly to the first boom section 2
at the inner end thereof, as illustrated in Figs 3 and 4. In the latter case, the
first point 11 of the first transmission member 10 is easily accessible at the inner
end of the boom 1', which makes it easy to adjust the tension of the first transmission
member 10 and thereby facilitates the installation and maintenance of the inner drive
system of the boom.
[0022] The first and second pulleys 13, 23 are with advantage rotatably mounted to an elongated
support unit 40, 40', which is fixed to the rear part of the second boom section 3,
i.e. at the inner end thereof, and which extends axially in the inner space 5 of the
boom sections. The first pulley 13 is mounted at the outer end of the support unit
40, 40' and the second pulley 23 is mounted at the inner end thereof. The support
unit 40, 40' is suitably provided with one or several sliding elements 41 at its outer
end, each sliding element 41 abutting against an inner sliding surface of the third
boom section 4 so as support the outer end of the support unit slidingly against the
third boom section 4.
[0023] In the embodiment illustrated in Figs 1 and 2, the support unit 40 is secured to
the second boom section 3 by means of an attachment 9 and it is arranged to move along
the elongated element 50 when the second boom section 3 is displaced axially in relation
to the first boom section 2. The elongated element 50 may be supported by the support
unit 40 via a first bracket 42 arranged at the inner end of the support unit and rest
against this bracket 42 via a sliding element 43 arranged on the bracket 42, as illustrated
in Figs 1 and 2. In the example illustrated in Figs 1 and 2, the sliding element 41
provided at the outer end of the support unit 40 is mounted to a second bracket 44,
which is arranged at the outer end of the support unit 40. The elongated element 50
extends through a cavity in the first bracket 42 and will also extend through a cavity
in the second bracket 44 when the boom is in the retracted position.
[0024] In the embodiment illustrated in Figs 1 and 2, the above-mentioned first points 11,
21 of the first and second transmission members 10, 20 are fixed to a holder 51 secured
to the elongated element 50 at the outer end thereof. The holder 51 may abut against
the support unit 40 via sliding elements 52 arranged on the holder 51. The above-mentioned
second points 12, 22 of the first and second transmission members 10, 20 are fixed
to another holder 53 secured to the third boom section 4 at the inner end thereof.
The holder 53 may abut against the support unit 40 via sliding elements 54 arranged
on the holder 53.
[0025] In the embodiment illustrated in Figs 3-12, the boom 1' comprises an elongated, flexible
third transmission member 30 (see Figs 7 and 12) in the form of a belt or cable or
chain or the like, which is arranged in the inner space 5 of the boom sections in
parallel to the second transmission member 20. This third transmission member 30 has
a first point (not shown) fixed in relation to the first boom section 2 and a second
point 32 fixed in relation to the third boom section 3. The transmission member 30
extends inside the boom sections between its first and second points over a pulley
33, in the following denominated third pulley, which is fixed in axial position in
relation to the second boom section 3. The third pulley 33 is arranged to act on the
third transmission member 30 so as to displace said second point 32 of the third transmission
member and thereby the third boom section 4 axially inwards in relation to the second
boom section 3 when the second boom section is displaced axially inwards in relation
to the first boom section 2 under the effect of the actuating member 6. The second
pulley 23 and the third pulley 33 are mutually concentric and rotatably mounted to
the support unit 40' on opposite sides thereof symmetrically in relation to the centre
axis of the support unit, as illustrated in Fig 12. In this case, the first pulley
13 is mounted in a plane which extends through the centre axis of the support unit
and forms the plane of symmetry for the second and third pulleys 23, 33. Said first
point of the third transmission member 30 is fixed to the elongated element 50 at
the outer end thereof at the same axial position along the elongated element as the
first point 21 of the second transmission member 20.
[0026] In the embodiment illustrated in Figs 3-12, the support unit 40' comprises a body
part formed by the cylinder part 6a of the actuating member. The second and third
pulleys 23, 33 are rotatably mounted to this cylinder part 6a on opposite sides thereof,
as illustrated in Figs 7-9 and 12. At its inner end, the cylinder part 6a is provided
with two projections 45, which extend from the cylinder part on opposite sides thereof.
These projections 45 are received in seats 7 provided on the inner wall of the second
boom section 3, as illustrated in Fig 12, so as to thereby secure the cylinder part
6a to the second boom section 3. The support unit 40' further comprises a bracket
46 secured to the outer end of the cylinder part 6a, the first pulley 13 being rotatably
mounted to this bracket 46. Sliding elements 41 are mounted on the outside of a frame
47 secured to the bracket 46 so as to allow the bracket to be slidingly supported
in relation to the inner wall of the third boom section 4.
[0027] The boom may comprise one or several flexible conduits 60 in the form of hoses or
cables arranged in the inner space 5 of the boom sections. Such a conduit 60 could
for instance be a hose for supplying compressed air or hydraulic fluid to a tool carried
by the boom at the outer end thereof and for return of hydraulic fluid from such a
tool. Such a conduit 60 could also be an electric or optical cable. In the embodiment
illustrated in Figs 3-12, the respective conduit 60 has a first point 61 fixed in
relation to the first boom section 2 and a second point 62 fixed in relation to the
third boom section 4. The conduit 60 extends inside the boom sections between said
first and second points 61, 62 over a pulley 63 which is fixed in axial position in
relation to the second boom section 3. The pulley 63 is arranged to act on the conduit
60 so as to keep the conduit stretched out and prevent it from slackening when the
boom sections are axially displaced in relation to each. The pulley 63 is located
closer to the outer end of the boom as compared to said first and second points 61,
62 of the conduit 60. Thus, the conduit 60 extends forwards from the first point 61
in the direction towards the outer end of the boom, around its pulley 63 and then
backwards from the pulley 63 to the second point 62 in the direction towards the inner
end of the boom. The pulley 63 is mounted to the bracket 46 at the outer end of the
support unit 40' and is suitably concentric with the first pulley 13, as illustrated
in Figs 7 and 12. In the example illustrated in Figs 7-12, the boom comprises two
pulleys 63 for conduits arranged on opposite sides of the first pulley 13. The respective
conduit 60 may be connected to a rigid pipe 64, which is mounted to the third boom
section 4 so as to extend from the second point 62 of the conduit to the outer end
of the third boom section.
[0028] All the pulleys 13, 23, 33, 63 are with advantage carried by the support unit 40'
so as to allow the pulleys and the support unit to be jointly mounted to the second
boom section 3 as a preassembled assembly. Fig 7 shows such a preassembled assembly
70 comprising:
- a base 71;
- a combined actuating member and support unit comprising a piston rod 6b and a cylinder
part 6a;
- the above-mentioned mounting projections 45 protruding from opposite sides of the
cylinder part 6a;
- the above-mentioned rigid elongated element 50 secured to the base 71;
- the above-mentioned first transmission member 10 secured at one end to the base 71
and at the other end to a slide member 73 slidingly arranged on top of the cylinder
part 6a;
- the above-mentioned second and third transmission members 20, 30, each of which being
secured at one end to the elongated element 50 via an attachment 72 provided at the
outer end of the elongated element and at the other end to the slide member 73;
- the above-mentioned second and third pulleys 23, 33 rotatably mounted to the cylinder
part 6a on opposite sides thereof;
- the above-mentioned bracket 46 provided at the outer end of the cylinder part 6a;
- the above-mentioned frame 47 with sliding elements 41 provided at the outer end of
the bracket 46; and
- the above-mentioned first pulley 13 rotatably mounted to the bracket 46.
[0029] The preassembled assembly 70 may also be provided with one or several flexible conduits
60, as illustrated in Fig 8. In the illustrated example, each conduit 60 is secured
at one end to a holder 74 mounted to the above-mentioned slide member 73 and at the
other end to the base 71. Each conduit 60 extends over a pulley 63 rotatably mounted
to the bracket 46 and is connected to a pipe 64, which is secured at one end to the
holder 74 and at the other end is to be secured to the outer end of the third boom
section 4.
[0030] The assembly 70 is mounted to an outer boom section 4 by being inserted with the
frame 47 first into the inner cavity of the boom section via the open inner end of
the boom section 4, as illustrated in Fig 9. The slide member 73 is then secured to
this boom section 4. Thereafter, the assembly 70 and the outer boom section 4 are
together mounted to an intermediate boom section 3 by being inserted with the base
71 first into the inner cavity of the intermediate boom section 3 via the open outer
end of the boom section 3, as illustrated in Fig 10. The cylinder part 6a is then
secured to the intermediate boom section 3 via the mounting projections 45. Finally,
the assembly 70, the outer boom section 4 and the intermediate boom section 3 are
together mounted to an inner boom section 2 by being inserted with the base 71 first
into the inner cavity of the inner boom section 2 via the open outer end of the boom
section 2, as illustrated in Fig 11. The base 71 and the piston rod 6b are then secured
to the inner boom section 2. Thus, this boom 1' can be assembled and disassembled
in a very simple and convenient manner, which will facilitate the installation of
the drive system of the boom and the maintenance of the boom and its drive system.
[0031] The telescopic boom according to the present invention may constitute a crane boom,
in which case the first boom section 2 could be pivotally mounted to a part of a crane,
for instance a vehicle crane, so as to be pivotable about a horizontal axis in relation
to that crane part. In this case, the third boom section 4 may be designed to carry
a load in a load suspension point located at its outer end. The telescopic boom according
to the invention may alternatively constitute an extension boom for positioning a
support leg in the horizontal direction in relation to the chassis of a trailer or
a vehicle in the form of a lorry or the similar. In this case, the first boom section
2 is mounted to the chassis of the trailer/vehicle and a vertically extendable support
leg is secured to the outer end of the third boom section 4.
[0032] The invention is of course not in any way restricted to the embodiments described
above. On the contrary, many possibilities to modifications thereof will be apparent
to a person with ordinary skill in the art without departing from the basic idea of
the invention as defined in the appended claims. The boom may for instance comprise
more than three boom sections if so desired.
1. A telescopic boom (1; 1') comprising:
- a first boom section (2);
- a second boom section (3) mounted to the first boom section (2) so as to be axially
displaceable in relation to the first boom section;
- a third boom section (4) mounted to the second boom section (3) so as to be axially
displaceable in relation to the second boom section; and
- an actuating member (6) acting on the second boom section (3) for displacing the
second boom section axially in relation to the first boom section (2),
characterized in:
- that the boom (1; 1') comprises an elongated, flexible first transmission member (10),
which is arranged inside the boom sections (2, 3, 4) and has a first point (11) fixed
in relation to the first boom section (2) and a second point (12) fixed in relation
to the third boom section (4);
- that the first transmission member (10) extends inside the boom sections between its first
and second points (11, 12) over a first pulley (13), which is fixed in axial position
in relation to the second boom section (3), the first pulley (13) being arranged to
act on the first transmission member (10) so as to displace said second point (12)
of the first transmission member (10) and thereby the third boom section (4) axially
outwards in relation to the second boom section (3) when the second boom section (3)
is displaced axially outwards in relation to the first boom section (2) under the
effect of the actuating member (6);
- that the boom (1; 1') comprises an elongated, flexible second transmission member (20),
which is arranged inside the boom sections (2, 3, 4) and has a first point (21) fixed
in relation to the first boom section (2) and a second point (22) fixed in relation
to the third boom section (4); and
- that the second transmission member (20) extends inside the boom sections between its
first and second points (21, 22) over a second pulley (23), which is fixed in axial
position in relation to the second boom section (3), the second pulley (23) being
arranged to act on the second transmission member (20) so as to displace said second
point (22) of the second transmission member (20) and thereby the third boom section
(4) axially inwards in relation to the second boom section (3) when the second boom
section (3) is displaced axially inwards in relation to the first boom section (2)
under the effect of the actuating member (6).
2. A telescopic boom according to claim 1, characterized in that the first pulley (13) and the second pulley (23) are mounted to an elongated support
unit (40: 40'), which is fixed to the second boom section (3) at the inner end thereof
and extends axially inside the second and third boom sections (3, 4), the first pulley
(13) being mounted at the outer end of the support unit (40: 40') and the second pulley
(23) being mounted at the inner end of the support unit (40: 40').
3. A telescopic boom according to claim 2, characterized in that the support unit (40: 40') is provided with one or several sliding elements (41)
at its outer end, each sliding element (41) abutting against an inner sliding surface
of the third boom section (4) so as support the outer end of the support unit (40:
40') slidingly against the third boom section (4).
4. A telescopic boom according to claim 2 or 3,
characterized in:
- that the boom (1') comprises an elongated, flexible third transmission member (30) extending
in parallel to the second transmission member;
- that the third transmission member (30) is arranged inside the boom sections (2, 3, 4)
and has a first point fixed in relation to the first boom section (2) and a second
point (32) fixed in relation to the third boom section (4);
- that the third transmission member (30) extends inside the boom sections between its first
and second points over a third pulley (33), which is fixed in axial position in relation
to the second boom section (3), the third pulley (33) being arranged to act on the
third transmission member (30) so as to displace said second point (32) of the third
transmission member (30) and thereby the third boom section (4) axially inwards in
relation to the second boom section (3) when the second boom section (3) is displaced
axially inwards in relation to the first boom section (2) under the effect of the
actuating member (6);
- that the second pulley (23) and the third pulley (33) are mutually concentric and mounted
to the support unit (40') on opposite sides thereof symmetrically in relation to the
centre axis of the support unit; and
- that the first pulley (13) is mounted in a plane which extends through the centre axis
of the support unit (40') and forms the plane of symmetry for the second and third
pulleys (23, 33).
5. A telescopic boom according to any of claims 2-4,
characterized in that the actuating member (6) comprises:
- a cylinder part (6a), which is fixed in axial position in relation to the second
boom section (3) and which constitutes a body part of the support unit (40'),
- a piston, which is mounted inside the cylinder part (6a) so as to be axially displaceable
in relation to the cylinder part, and
- a piston rod (6b), which is secured to the piston and fixed in axial position in
relation to the first boom section (2).
6. A telescopic boom according to claim 5 in combination with claim 4, characterized in that the second pulley (23) and the third pulley (33) are mounted to said cylinder part
(6a) on opposite sides thereof.
7. A telescopic boom according to claim 6, characterized in that the support unit (40') comprises a bracket (46) secured to the outer end of said
cylinder part (6a), the first pulley (13) being mounted to this bracket (46).
8. A telescopic boom according to any of claims 1-7,
characterized in:
- that the boom (1') comprises at least one flexible conduit (60) in the form of a hose
or cable, which is arranged inside the boom sections (2, 3, 4) and has a first point
(61) fixed in relation to the first boom section (2) and a second point (62) fixed
in relation to the third boom section (4); and
- that said conduit (60) extends inside the boom sections between its first and second points
(61, 62) over a pulley (63), which is fixed in axial position in relation to the second
boom section (3) and arranged to act on the conduit (60) so as to keep the conduit
stretched out and prevent it from slackening when the boom sections are axially displaced
in relation to each other.
9. A telescopic boom according to claim 8 in combination with claim 2, characterized in that the pulley (63) for said conduit (60) is mounted to the support unit (40') at the
outer end thereof.
10. A telescopic boom according to claim 9, characterized in that the pulley (63) for said conduit (60) is concentric with the first pulley (13).
11. A telescopic boom according to any of claims 1-10,
characterized in:
- that the boom comprises a rigid elongated element (50), which extends axially inside the
boom sections (2, 3, 4) and is fixed in axial position in relation to the first boom
section (2); and
- that said first point (21) of the second transmission member (20) is fixed to said elongated
element (50) at the outer end thereof.
12. A telescopic boom according to claim 11 in combination with claim 4, characterized in that said first point of the third transmission member (30) is fixed to said elongated
element (50) at the outer end thereof.