FAIL-SAFE SPRING
Field of the invention
The present invention relates to a downhole tool extending in a longitudinal
direction, comprising a tool housing; an arm assembly movable between a
retracted position and a projecting position in relation to the tool housing; and an
arm activation assembly for moving the arm assembly between the retracted
position and the projecting position. Furthermore, the invention relates to a
downhole system.
Background art
Downhole tools are used for operations inside boreholes of oil and gas wells.
Downhole tools operate in a very harsh environment and must be able to
withstand inter alia corroding fluids, high temperatures and high pressure.
To avoid unnecessary and expensive disturbances in the production of oil and
gas, the tools deployed downhole have to be reliable and easy to remove from
the well in case of a breakdown. Tools are often deployed at great depths several
kilometres down the well, and removing jammed tools are therefore a costly and
time-consuming operation.
Well tools are often part of a larger tool string containing tools with different
functionalities. A tool string may comprise both transportation tools for
transporting the tool string in the well and operational tools for performing
various operations downhole, e.g. centralising tools for centralising the tool or
tool string in the borehole, driving units for moving the tool or tool string in the
borehole and anchoring tools for anchoring the tool or tool string in the borehole.
The use of tools and/or units with extracting members for engaging the borehole
wall has potential risk of jamming in the borehole in case of a breakdown.
Extreme conditions such as very high pressures, high temperatures and an acidic
environment therefore place high demands on mechanical mechanisms in
downhole tools.
The above often results in a minimum use of such tools downhole to avoid
unwanted breaks in production times. Therefore, a need exists for downhole tools
that are relatively fail-safe and thus extractable from the borehole, also in case of
a breakdown.
Summary of the invention
It is an object of the present invention to wholly or partly overcome the above
disadvantages and drawbacks of the prior art. More specifically, it is an object to
provide an improved downhole tool wherein a spring member ensures a fail-safe
retraction of extracting members of the downhole tool.
The above objects, together with numerous other objects, advantages, and
features, which will become evident from the below description, are accomplished
by a solution in accordance with the present invention by a downhole tool
extending in a longitudinal direction, comprising:
a tool housing,
an arm assembly movable between a retracted position and a projecting
position in relation to the tool housing, and
an arm activation assembly for moving the arm assembly between the
retracted position and the projecting position,
wherein the arm activation assembly comprises:
a piston housing comprising a piston chamber, said piston chamber
extending in the longitudinal direction of the downhole tool,
a piston member arranged inside the piston chamber and engaged with
the arm assembly to move the arm assembly between the retracted
position and the projecting position, the piston member being movable in
the longitudinal direction of the downhole tool and having a first piston
face and a second piston face, the piston member being able to apply a
projecting force on the arm assembly by applying a hydraulic pressure
on the first piston face moving the piston in a first direction, and
a spring member applying a spring force to move the piston in a second
direction opposite the first direction.
In one embodiment, the arm activation assembly may comprise a fluid channel
and the hydraulic pressure may be applied to the first piston face with a
pressurised hydraulic fluid such as oil through the fluid channel.
In another embodiment, the spring member may be arranged in a spring
chamber and the piston may be arranged in a piston chamber.
Said piston housing may comprise a recess for receiving part of the shaft when
the piston moves.
Moreover, the shaft may extend in the piston chamber and into the spring
chamber.
Further, the piston member may divide the piston housing into a first and a
second section, the first section being filled with fluid for moving the piston
member.
The downhole tool according to the invention may further comprise a pump for
pressurising the pressurised hydraulic fluid for moving the piston in the first
direction.
Additionally, the downhole tool according to the invention may comprise an
electrical motor for driving the pump.
In one embodiment, the downhole tool may be connected with a wireline and the
electrical motor may be powered through the wireline.
Also, the downhole tool may comprise several arm assemblies and arm activation
assemblies and each of the arm assemblies may be moved by one of the arm
activation assemblies.
Additionally, the piston chamber and spring chamber may be arranged
substantially end-to-end in the longitudinal direction of the tool.
The piston chamber and the spring chamber may be arranged substantially sideby-
side in the longitudinal direction of the tool.
In one embodiment, the downhole tool according to the invention may further
comprise a control member arranged inside a coil of the spring.
In another embodiment, the piston may comprise a distal part with a reduced
diameter engageable with the spring member.
Said spring member may be is a coil spring, a helical spring, a bellows, a volute
spring, a leaf spring, a gas spring or a disc spring.
The downhole tool according to the invention may further comprise electrical
sensors for monitoring a pressure on the first piston face for producing a
feedback signal to a control system.
Moreover, the downhole tool according to the invention may comprise electrical
sensors for monitoring a position of the piston member for producing a feedback
signal to a control system.
The above-mentioned spring member may be preloaded before being
compressed by the piston during application of the hydraulic pressure on the first
piston face moving the piston in a first direction.
Also, the piston member may be connected with the arm assembly using a worm
shaft, a crank arm or a rack or a pivot joint or a recess in the piston member.
The present invention also relates to a downhole system, comprising:
-a wireline,
-a mating tool such as a driving unit and/or an operational tool, and
-a downhole tool as described above.
Further, the arm activation assembly of the downhole tool as described above
may comprise a crank arm, meaning that when the piston member is moved
back and forth in the longitudinal direction of the piston chamber, the piston
member will move the crank arm, and when the crank arm is moved, a crank
shaft is rotated around a rotation axis, and hence the arm assembly being
connected to the crank shaft is moved between a retracted position and a
projecting position, and wherein a force arm distance between the rotation axis
of the crank arm and a point of contact between the crank arm and the piston
member may be longer in the retracted position than in the projecting position,
meaning that a resulting projecting force applied to the arm assembly by the arm
activation assembly is decreasing from a high resulting projection force in the
retracted position towards a lower resulting projection force in the projecting
position.
Brief description of the drawings
The invention and its many advantages will be described in more detail below
with reference to the accompanying schematic drawings, which for the purpose of
illustration show some non-limiting embodiments and in which
Fig. 1 shows a cross-sectional view of an arm activation assembly,
Fig. 2 shows a cross-sectional view of an arm activation assembly in a projecting
position,
Fig. 3 shows a cross-sectional view of an arm activation assembly in a retracted
position,
Fig. 4 shows a cross-sectional view of another embodiment of the arm activation
assembly,
Fig. 5 shows a cross-sectional view of another embodiment of the arm activation
assembly,
Fig. 6 shows, for illustrative purposes, a top view of part of a downhole tool with
one arm assembly in a projecting position and another arm assembly in a
retracted position,
Fig. 7 shows, for illustrative purposes, a top view of part of a downhole tool with
one arm assembly in a projecting position and another arm assembly in a
retracted position, wherein the arm assemblies comprise a wheel,
Fig. 8 shows a downhole system comprising an arm activation assembly for
moving an arm assembly in a driving section,
Fig. 9 shows a tool string comprising an arm activation assembly for moving an
arm assembly in a driving section.
Fig. 10 shows a cross-sectional view of an arm activation assembly,
Fig. 11 shows a cross-sectional view of an arm activation assembly,
Fig. 12 shows a cross-sectional view of an arm activation assembly,
Fig. 13a shows a cross-sectional view of an arm activation assembly in a
retracted position,
Fig. 13b shows a cross-sectional view of an arm activation assembly in a
projecting position,
Fig. 14a shows a perspective view of an arm activation assembly and an arm
assembly in a retracted position, and
Fig. 14b shows a perspective view of an arm activation assembly and an arm
assembly in a projecting position.
All the figures are highly schematic and not necessarily to scale, and they show
only those parts which are necessary in order to elucidate the invention, other
parts being omitted or merely suggested.
Detailed description of the invention
Fig. 1 shows an arm activation assembly 40 for moving an arm assembly 60
which is shown in Fig. 6 between a retracted position and a projecting position.
The arm activation assembly 40 is arranged in a tool housing 54 of a downhole
tool being part of a tool string 10. An example of such tool string is shown in Fig.
8. The arm activation assembly 40 comprises a piston housing 41, a piston
chamber 42 extending in a longitudinal direction of the downhole tool. A piston
member 47 is arranged inside the piston chamber and the piston member is
engaged with the arm assembly. When the piston member 47 is moved back and
forth in the longitudinal direction of the piston chamber, the piston member will
move a crank arm 72 of an engaging crank 70. When moving the crank arm 72,
a crank shaft 7 1 is rotated around a rotation axis 32, and hence the arm
assembly is moved between a retracted position and a projecting position. The
crank 70 connects the piston member 47 with the arm assembly converting a
transverse motion of the piston member to a rotation force acting on the arm
assembly. In an arm activation assembly of the downhole tool, the arm assembly
may be directly connected with a piston member 47. As shown in the drawings,
the crank arm is connected with the piston member by the crank arm being
arranged in a recess in the piston member and engaging the piston member by
engaging means 83. The crank arm may, however, be connected to the piston
member in any suitable way known to the person skilled, such as by using a rack
also known as a toothed rack or gear-rack, or a worm shaft or a sliding pivot
joint.
The piston member is dividing the piston chamber into a first section 42a and a
second section 42b, the first section being in fluid communication with an
activation fluid channel 80. A hydraulic fluid such as oil may be injected through
the fluid channel 80 into the first section 42a of the chamber 42, thereby
applying a hydraulic pressure on a first piston face 48 of the piston member 47. A
spring member 44 is arranged in the second section 42b of the chamber between
a second piston face 49 of the piston member and a distal end face 42d of the
piston chamber. The spring member 44 applies a spring force to the second
piston face 49. The hydraulic fluid moves the piston in a first direction, and the
spring member 44 moves the piston in a second direction opposite the first
direction.
As shown, the arm activation assembly in Fig. 1 has the piston member 47 which
may comprise a piston part 47a and a piston shaft part 47b. As shown, the spring
member may then circumscribe the piston shaft part in such a way that the
travel of the spring member 44 during compression and decompression is well
controlled. Furthermore, the piston shaft part may engage a recess 82 in the
piston housing 4 1 to further improve control of the travel of the piston member
within the piston chamber. The control of the travel of the piston member is
improved since a distal end of the piston shaft part abuts the walls of the recess
during travel of the piston. The piston comprises a distal part 8 1 with a reduced
diameter engageable with the spring member. Furthermore, the piston member
may be connected with the arm assembly using a worm shaft, a rack or a pivot
joint or a recess 471 in the piston member.
Fig. 2 shows the arm activation assembly in a projecting position. When the arm
assembly needs to be projecting during downhole operations, a hydraulic
pressure is applied to the first piston face 48 of the piston member 47 by
pressurising a hydraulic fluid in the first section 42a of the piston chamber 42.
When the hydraulic pressure is applied to the first piston face, the piston member
moves towards the distal end face 42d of the piston chamber, thereby
compressing the spring member 44. In order for the hydraulic pressure to move
the piston member and thereby the arm activation assembly to the projecting
position, the hydraulic pressure must exceed a spring force applied by the spring
member 44 on the second piston face 49 and additional frictional forces
stemming from the travel of the piston member in the piston chamber.
Furthermore, the movement of the piston member results in a movement of the
crank arm 72 since the piston member engages the crank arm. When the crank
arm is moved in the longitudinal direction of the piston chamber towards the
distal end face 42d, the crank shaft 7 1 will rotate around the rotation axis 32 of
the crank 70.
Fig. 3 shows the arm activation assembly in a retracted position. When the arm
assembly needs to be retracted during downhole operations, the hydraulic
pressure, which during projection was applied to a first piston face 48 of the
piston member 47 by pressurising a hydraulic fluid in the first section, is then
removed. When the hydraulic pressure is removed from the first section, the
hydraulic pressure will no longer exceed the spring force applied by the spring
member on the second piston face, and the piston member will therefore begin to
move towards the distal end face 42c of the piston chamber forced by the spring
member, thereby decompressing the spring member. In case of unintentional
drops of hydraulic pressure in the first section of the chamber, the spring
member acts as a fail-safe so that the tool can always be retracted from the well.
When working with downhole operations, jamming of downhole tools in a
borehole is one of the most aggravating problems, which may cause downtime in
the production, and even worse it may shut down a borehole if the jammed
downhole tool cannot subsequently be removed. If the hydraulic pressure in the
first section is lost, the arm activation assembly 40 will always move to a
retracted position due to the spring member 44. Being unable to project the arm
assembly with the arm activation assembly is of course inexpedient but it is not
critical to the downhole operation since the tool string is merely retracted to the
surface by a wireline 9 via a top connector 13 or a coiled tubing 9 connecting the
tool string to the surface (shown in Fig. 8). Furthermore, a downhole tool may
comprise several arm assemblies and if one does not project, others will.
In Fig. 3, the arm activation assembly 40 further comprises preloading means 85
for preloading the spring member 44. The preloading means allows assembly of
the arm activation assembly with an uncompressed spring member 44, where the
spring member then, subsequent to the assembly of the arm activation
assembly, can be preloaded using the preloading means. The preloading means
may comprise a screw 85a or a plurality of screws 85a and a washer 85b. Apart
from making the assembly of the arm activation assembly more convenient, the
preloading means may furthermore allow the user to preload, i.e. compress, the
spring member to a certain degree to accommodate for certain requirements to
the retraction mechanism of the arm activation assembly. An example of a
situation demanding a high retraction force may be if the arm assembly has been
used to anchor the tool string in a production casing or the borehole and
therefore is sticking to the surface of the production casing or wall of the
borehole. On the other hand, a lower retraction force may be needed if for
example the arm assembly is used for wheels 62 in a driving section 11 (see Fig.
7). The retracting force in this situation may not necessarily have to be very
high, and a low retraction force exerted by the spring member 44 may be more
appropriate for providing a slower retraction of the wheels.
In the arm activation assembly shown in Fig. 4, the spring member is arranged in
a spring chamber 42a and the piston is arranged in a piston chamber 42. The
mounting of springs during production and/or maintenance of separable
equipment including springs present a potential risk to the user. Therefore,
enclosure of the spring member in a separate chamber may be advantageous to
the handling and maintenance of such equipment, especially in a case where a
very high preloading force of the spring is required.
When the spring member is arranged in a separate chamber such as shown in
Fig. 4 and Fig. 5, the spring force from the spring member still has to be capable
of engaging the piston member in the piston chamber. In one embodiment, the
piston shaft part may enter the spring chamber 42a through a connection hole
between the piston chamber and the spring chamber such as shown in Fig. 4.
Alternatively, the engagement of the piston member and the spring member may
be facilitated by an intermediate piston member 86 sealing off the spring
chamber as shown in Fig. 5.
Fig. 6 is an illustration of a part of the downhole tool with one arm assembly in a
projecting position and another arm assembly in a retracted position. During
downhole operations the arm assemblies of the downhole tool would typically all
be in a projecting or a retracted position. The arm assembly may be used for
several purposes during downhole operations such as tool centralising in the
borehole 4 in a formation 2 or inside a production casing 6. Furthermore, an arm
assembly may be used for anchoring, e.g. to ensure weight on bit during
horizontal drilling, during downhole stroking or during operations perforating the
production casing when setting up production zones.
The crank shaft may be connected to the arm member 6 1 by means such as a
toothed crank shaft pattern mating with a similar pattern (not shown) in a bore in
the arm member. The crank shaft and the arm member hereby interlock whereby
the rotation force is transferred from the crank shaft to arm member.
Fig. 7 is another illustration of a part of the downhole tool with one arm assembly
in the projecting position and another arm assembly in a retracted position. The
arm assembly comprises an arm member and furthermore a wheel 62 for driving
the tool string during downhole operations. An arm member 6 1 of the arm
assembly 60 is seen in the left side of Fig. 7 in the projecting position and in this
situation engaging an inner wall of a production casing 6. Furthermore, it is
shown in Fig. 7 that an elongate axis of the arm member 6 1 has a projection
angle Al of less than ninety degrees with respect to the longitudinal axis of the
tool string. In this way, the retraction of the arm assembly will not have a
barbing function when pulling the wireline 9 or coiled tubing 9. Pulling the
wireline or coiled tubing will therefore contribute to the retraction of the arm
assembly if the projection angle is less than ninety degrees. As shown in Fig. 7,
the crank shaft 7 1 is arranged away from a centre axis of the arm assembly. The
intention is to be able to reach as far as possible away from the tool string,
thereby being able to operate with larger casings.
The number of driving units 11 and/or the number of wheels 62 in a tool string
may be varied depending on the required pulling force, e.g. high pulling force is
required when operating a heavy tool string. Therefore, a number of arm
activation assemblies and arm assemblies may be arranged in a driving unit
and/or more than one driving unit may be arranged in the tool string.
The downhole tool string 10 shown in Fig. 8 comprises an electrical motor 17 for
moving a hydraulic pump 18. The hydraulic pump 18 may be used to generate a
pressurised hydraulic fluid. The driving unit 11 is connected with a compensating
device 20 for compensating the pressure within the driving unit so that a high
pressure difference between the fluid surrounding the tool string 10 and the
inside of the tool string 10, e.g. the inside of the driving unit, does not result in
the driving unit housing bulging outwards or collapsing inwards. The driving unit
11 may furthermore be connected with an operational tool 12 through a
connector 14. The pressurised fluid may be injected through the fluid channel 80
and into the first section of the chamber to project the arm assembly by means
of the arm activation assembly. The electric motor 17 may be powered from the
surface by a wireline 9, or alternatively the electric motor may be powered by
batteries (not shown) arranged in the tool string. During coiled tubing operations
well-known to any person skilled in the art, the hydraulic pump may be replaced
by a hydraulic pump at the surface generating a pressurised fluid at the surface
which is pumped through a coiled tubing 9 to the downhole tool string. Coiled
tubing operations are typically limited to smaller depths of boreholes due to the
weight of the coiled tubing. At very large depths and in horizontal parts of the
well, wireline operations are therefore more appropriate than coiled tubing
operations.
The shown tool string comprises a downhole tool in the form of a driving unit 11
for moving the tool string forward downhole. The downhole tool extends in a
longitudinal direction and comprises a tool housing, arm assemblies and arm
activation assemblies. The tool string shown in Fig. 9 is moved forward by several
wheels projecting towards the casing or side walls of the well. The wheels are
mounted on the arm member 6 1 in such a way that they can be moved between
a retracted position and a projecting position. When the wheels turn, the tool
string is moved forward deeper into the hole, and typically the wireline or the
coiled tubing is used to retract the tool string back towards the surface, since it is
faster than using downhole propagation means such as the driving unit.
Figs 10-12 show cross-sectional views of the arm activation assembly 40 in a
retracted position (see Fig. 10), in an intermediate position (see Fig. 11) and in a
projecting position (see Fig. 12). As shown in Figs. 10-12, the spring member
may be arranged in a different chamber than the piston member 47. In order to
minimise the use of space in the downhole tool in the longitudinal direction, the
spring member may be arranged substantially side-by-side the piston member 47
(see Figs. 13a and 13b) instead of substantially end-to-end (see Figs. 1-5). If the
spring member and piston member 47 are arranged side-by-side, the spring
member may apply a retracting force to the crank arm 72 by an intermediate
member 45. Alternatively, the spring member may apply a retracting force
directly to the arm assembly (not shown).
As shown in Figs. 10-12, the distance Dl, D2, D3 between the rotation axis 32
and a point of contact between the crank arm 72 and the piston member 47 is
preferably longer in the retracted position than in the projecting position,
meaning that a resulting projecting force applied to the arm assembly by the arm
activation assembly 40 is decreasing from a high resulting projection force in the
retracted position towards a lower resulting projection force in the projecting
position. This decreasing resulting projecting force ensures that the tool string is
well centralised in the production casing during projection of the arm assembly,
i.e. the further out the arm assembly is projecting, the smaller the resulting
projecting force is. This means that the resulting force will always be highest on
the parts of the arm assembly which are less projecting, thereby always ensuring
that the tool string will automatically be well centralised in the production casing
or well bore.
Fig. 13a shows a cross-sectional view of an arm activation assembly 40 in a
retracted position, where the piston member 47 and spring member 44 are
arranged substantially side-by-side in the longitudinal direction of the tool string.
As seen, this may save space in the longitudinal direction. In embodiments where
the spring member 44 is not arranged in direct contact with the piston member
47, an intermediate member 45, such as the one shown in Figs. 13a, 13b, 14a
and 14b, may be arranged between the piston member 47 and spring member
44. Thereby the spring member 44 is still allowed to apply the spring force
opposite the projection force of the piston member to provide fail-safe retraction
of the arm assembly 60. Fig. 13b shows a cross-sectional view of the arm
activation assembly 40 of Fig. 13a in a projecting position. Figs. 14a and 14b
show perspective views of the downhole tool shown in Figs. 13a and 13b, also in
a retracted and projecting position, respectively. As shown in Figs. 14a and 14b,
the spring member 44 is not required to be arranged in a confined chamber as
long as the spring force acts opposite the projecting force so that the arm
assembly 60 is retracted if hydraulic pressure on the piston member 47 is lost,
ensuring a fail-safe retraction mechanism independent of hydraulic pressure in
the tool.
The fluid transferred into the first section of the chamber may be branched out
through other fluid channels to reach an adjacent arm activation assembly (not
shown) in a driving unit. The arm activation assembly may thus comprise an
integrated fluid circuit in the form of fluid channels provided in the walls of the
piston housing. Several activation assemblies may then be combined to provide a
larger fluid circuit without the need of external piping connecting the individual
activation assemblies. Fluid channels of subsequent piston houses are joined by
connectors (not shown) creating tight fluid joints.
The spring member 44 may be any type member exerting a spring force on the
second piston face 49 such as a coil spring, helical spring, bellow, volute spring,
leaf spring, gas spring or disc spring. The spring type may be used for designing
an appropriate spring force exerted on the piston member such as a constant
spring force or a spring force that increases during projection of the arm
assembly, so that the highest spring force is obtained at the outermost position
of the arm assembly.
By introducing intelligent sensors 84 (shown in Fig. 1) such as pressure gauges,
switches for determining position of the piston member 47 and/or crank arm 72,
feedback signals may be fed back to the user and/or to controlling electronics 15,
16 in the tool string (shown in Fig. 8).
Although the invention has been described in the above in connection with
preferred embodiments of the invention, it will be evident for a person skilled in
the art that several modifications are conceivable without departing from the
invention as defined by the following claims.
Claims
1. A downhole tool (10) extending in a longitudinal direction, comprising:
a tool housing (54);
- an arm assembly (60) movable between a retracted position and a
projecting position in relation to the tool housing; and
an arm activation assembly (40) for moving the arm assembly between
the retracted position and the projecting position;
wherein the arm activation assembly comprises:
- a piston housing (41) comprising a piston chamber (42), said piston
chamber extending in the longitudinal direction of the downhole tool,
a piston member (47) arranged inside the piston chamber and engaged
with the arm assembly to move the arm assembly between the retracted
position and the projecting position, the piston member being movable in
the longitudinal direction of the downhole tool and having a first piston
face (48) and a second piston face (49), the piston member being able
to apply a projecting force on the arm assembly by applying a hydraulic
pressure on the first piston face moving the piston in a first direction,
and
- a spring member (44) applying a spring force to move the piston in a
second direction opposite the first direction.
2. A downhole tool according to claim 1, wherein the arm activation assembly
comprises a fluid channel (80) and the hydraulic pressure is applied to the first
piston face with a pressurised hydraulic fluid such as oil through the fluid
channel.
3. A downhole tool according to claim 1 or 2, wherein the spring member is
arranged in a spring chamber (42a) and the piston is arranged in a piston
chamber (42).
4. A downhole tool according to any of claims 1-3, wherein the piston housing
comprises a recess (82) for receiving part of the shaft when the piston moves.
5. A downhole tool according to any of claims 1-4, wherein the shaft extends
in the piston chamber and into the spring chamber.
6. A downhole tool according to any of claims 1-5, wherein the piston member
divides the piston housing into a first and a second section, the first section being
filled with fluid for moving the piston member.
7. A downhole tool according to any of claims 1-6, further comprising a pump
(18) for pressurising the pressurised hydraulic fluid for moving the piston in the
first direction.
8. A downhole tool according to any of claims 1-7, wherein the downhole tool
is connected with a wireline (9) and an electrical motor (17) is powered through
the wireline.
9. A downhole tool according to any of claims 1-8, wherein the downhole tool
comprises several arm assemblies and arm activation assemblies and each of the
arm assemblies are moved by one of the arm activation assemblies.
10. A downhole tool according to any of claims 1-9, wherein the piston chamber
and spring chamber are arranged substantially end-to-end in the longitudinal
direction of the tool.
11. A downhole tool according to any of claims 1-10, wherein the piston
chamber and spring chamber are arranged substantially side-by-side in the
longitudinal direction of the tool.
12. A downhole tool according to any of claims 1-11, wherein the piston
comprises a distal part (81) with a reduced diameter engageable with the spring
member.
13. A downhole tool according to any of claims 1-12, further comprising
electrical sensors for monitoring a position of the piston member for producing a
feedback signal to a control system.
14. A downhole tool according to any of claims 1-13, wherein the spring
member is preloaded before being compressed by the piston during application of
the hydraulic pressure on the first piston face moving the piston in a first
direction.
15. A downhole tool according to any of claims 1-14, wherein the piston
member is connected with the arm assembly using a worm shaft, a rack or a
pivot joint or a recess (471) in the piston member.
16. A downhole system, comprising:
- a wireline (9),
- a mating tool such as a driving unit (11) and/or an operational tool
(12), and
- a downhole tool (10) according to any of claims 1-15.
17. A downhole tool according to any of claims 1-15, wherein the arm activation
assembly comprises a crank arm (72), meaning that when the piston member
(47) is moved back and forth in the longitudinal direction of the piston chamber,
the piston member will move the crank arm (72), and when the crank arm (72) is
moved, a crank shaft (71) is rotated around a rotation axis (32), and hence the
arm assembly being connected to the crank shaft (71) is moved between a
retracted position and a projecting position, and wherein a force arm distance
between the rotation axis (32) of the crank arm (72) and a point of contact
between the crank arm and the piston member is longer in the retracted position
than in the projecting position, meaning that a resulting projecting force applied
to the arm assembly by the arm activation assembly is decreasing from a high
resulting projection force in the retracted position towards a lower resulting
projection force in the projecting position.