TECHNICAL FIELD

The present invention relates to overhead doors and in particular to a torsion spring tensioning tool for tensioning a torsion spring of a counterbalancing mechanism of an overhead door.

BACKGROUND ART

In overhead doors a counterbalancing mechanism is usually used to counterbalance the weight of the door in order to reduce the force required for operating the door. This reduces the human effort or the motor power required to open the door. The counterbalancing mechanism usually comprises one or two torsion springs arranged around a shaft. One end of the torsion spring is fixed e.g. by a stationary cone. The other end of the torsion spring usually comprises a winding cone that is securable to the shaft by tightening screws and sometimes by a key. The winding cone is commonly provided with four radial holes for winding of the spring either by hand operated rods or by a tensioning tool for tensioning of the spring by rotation of the torsion spring before securing the winding cone to the shaft.

One type of tensioning tool is described in US 8 616 093, where a torsion spring winding assembly comprises a coupling shaft structure for installation on a torsion spring winding cone, a gearbox assembly installed onto the coupling shaft structure and a sliding lever arm attached to the gearbox assembly and positioned against the inside of a garage door frame structure. The coupling shaft structure is comprised of two body halves that are fitted together by guiding pins and mating holes. Each body half has a winding hub portion. Each winding hub portion has two locking bolts hand tightened into winding bar slots on the winding cone. The gearbox assembly has a gearbox end cap that is pivotable into an open position. The gear box end cap fits around the coupling shaft structure. The gearbox assembly is securable to the coupling shaft structure. A screw gun applies a rotational force to the gearbox assembly. Known tensioning tools are complicated to mount on the shaft of the counterbalancing mechanism and require a large number of operations to connect the tensioning tool to the torsion spring. Tensioning tools according to prior art also comprises several parts that are complex, weak and sensitive to wear. Thus, there exists a need for an improved tensioning tool.

SUMMARY OF THE INVENTION

One object of the present invention is to facilitate tensioning of a torsion spring of a counterbalancing mechanism. One object of the present invention is to facilitate connection of a tensioning tool to a torsion spring of a counterbalancing mechanism and/or releasing a tensioning tool from the torsion spring. One object of the present invention is to facilitate mounting of a tensioning tool on a shaft of a counterbalancing mechanism and/or removing a tensioning tool from the torsion spring. One object of the present invention is to reduce the time for connecting a tensioning tool to a torsion spring of a counterbalancing mechanism and/or releasing a tensioning tool from the torsion spring. One object of the present invention is to achieve a simplified tensioning tool. One object of the present invention is to achieve a tensioning tool having prolonged lifetime. One object of the present invention is to achieve a more robust tensioning tool.

These and further objects are achieved by a torsion spring tensioning tool for tensioning a torsion spring of a counterbalancing mechanism of an overhead door. The torsion spring tensioning tool comprises a housing, a gear wheel rotatably arranged in the housing and a gear mechanism adapted to rotate the gear wheel. The gear wheel is adapted to be mounted on a shaft of the counterbalancing mechanism. The gear wheel comprises a fastening means adapted to be connected to the torsion spring of the counterbalancing mechanism and transmit a rotational movement from the gear wheel to the torsion spring. The gear wheel comprises a first wheel segment and a second wheel segment, which second wheel segment is axially attachable to and axially detachable from the first wheel segment. The first wheel segment is adapted to be mounted on the shaft of the counterbalancing mechanism when the second wheel segment is in a detached state. The tensioning tool of the present invention facilitates tensioning of a torsion spring of a counterbalancing mechanism. The tensioning tool of the present invention facilitates connection of a tensioning tool to a torsion spring of a counterbalancing mechanism and release of a tensioning tool from the torsion spring. The tensioning tool of the present invention facilitates mounting of a tensioning tool on a shaft of a counterbalancing mechanism and removal of a tensioning tool from the torsion spring. The tensioning tool of the present invention reduces the time for connecting a tensioning tool to a torsion spring of a

counterbalancing mechanism and releasing a tensioning tool from the torsion spring. The tensioning tool of the present invention implies that a simplified tensioning tool is achieved. The tensioning tool of the present invention implies that a tensioning tool having prolonged lifetime is achieved. The tensioning tool of the present invention implies that a more robust tensioning tool is achieved. The tensioning tool of the present invention reduces the necessary space for connecting a tensioning tool to a torsion spring of a counterbalancing mechanism. The tensioning tool of the present invention implies that a counterbalancing mechanism can be mounted close to a ceiling. The tensioning tool of the present invention implies that a counterbalancing mechanism mounted close to a ceiling can be tensioned by a tensioning tool.

When the second wheel segment is detached, the first wheel segment of the gear wheel is mounted on the shaft of the counterbalancing mechanism. The fastening means of the gear wheel is connected to the torsion spring of the counterbalancing mechanism and transmits a rotational movement from the gear wheel to the torsion spring. Since the second wheel segment is axially attachable to and axially detachable from the first wheel segment, the second wheel segment is easily attached to and detached from the first wheel segment by a simple movement in one direction. No radial movement of the second wheel segment is necessary to release the second wheel segment. Thereby, the connection of a tensioning tool to and the release of a tensioning tool from a counterbalancing mechanism are facilitated and the times therefor are reduced. The necessary space for connecting a tensioning tool to a torsion spring of a counterbalancing mechanism is thereby also reduced and thus a counterbalancing mechanism can be mounted close to a ceiling and yet be tensioned by a tensioning tool. By having an axially attachable and axially detachable second wheel segment a simple, robust and durable construction can be utilized. In one aspect, the second wheel segment is adapted to interact with the first wheel segment when the second wheel segment is in an attached state such that the second wheel segment is fixed radially outwards in relation to the first wheel segment. Thereby, the second wheel segment is kept in place such that a properly shaped gear wheel is achieved, whereby proper and smooth operation of the tensioning tool is obtained. Also a simple, robust and long-lasting design is achieved.

In one aspect, the first wheel segment has a first radial profile and the second wheel segment has a second radial profile that corresponds to the first radial profile of the first wheel segment such that the second wheel segment is fixed radially outwards in relation to the first wheel segment when the second wheel segment is in the attached state. Thereby, the second wheel segment is kept in place in a simple way. The first and second wheel segments form a properly shaped gear wheel, whereby proper and smooth operation of the tensioning tool is obtained. A simple, robust and long-lasting design is achieved without any need for a complicated locking mechanism that is cumbersome to operate and/or is weak and risk failure and breakdown. The second wheel segment is easily attachable to and detachable from the first wheel segment.

In one aspect, one of the first radial profile and the second radial profile comprises a tongue and the other of the first radial profile and the second radial profile comprises a groove. By a tongue-and-groove design in the profile, the second wheel segment is easily and securely fixed radially outwards in relation to the first wheel segment. The second wheel segment is kept in place properly and the design is reliable, simple and robust. The second wheel segment is easily attachable to and detachable from the first wheel segment.

In one aspect, the second segment is adapted to be axially attachable to and axially detachable from the first wheel segment when the first wheel segment is mounted on the shaft of the counterbalancing mechanism and when the fastening means is connected to the torsion spring of the counterbalancing mechanism. Thereby, the second wheel segment is easily mountable to the counterbalancing mechanism during mounting of the tensioning tool and easily releasable from the counterbalancing mechanism during removal of the tensioning tool. The second wheel segment is easily attached to and detached from the first wheel segment by a simple movement in one direction and no radial movement of the second wheel segment is necessary to release the second wheel segment.

In one aspect, the housing is adapted to axially lock the second wheel segment in relation to the first wheel segment. Thereby, the second wheel segment is axially guided such that the gear wheel is properly shaped and the first and second wheel segments are securely kept together. This gives a simple, robust and reliable construction. The tensioning tool is also easily and rapidly mounted.

In one aspect, the housing encloses the circumferential periphery of the gear wheel and comprises a flange arranged along the circumference of the gear wheel, which flange is adapted to axially lock the first wheel segment and the second wheel segment. The flange easily locks the first and second wheel segments axially. Thereby, the mounting of the tensioning tool is facilitated. The flange is a robust and reliable way of locking the first and second wheel segments without the need for complicated and weak locking mechanisms.

In one aspect, the housing comprises a first housing part and a second housing part which are movable in relation to each other such that the gear wheel is detachable form the housing. By having a first and a second housing part that are movable in relation to each other the gear wheel can be released from the housing, which facilitates the mounting of the gear wheel, and in particular the first wheel segment, on the shaft of the counterbalancing mechanism. The first housing part, the second housing part and the first wheel segment of the gear wheel do not have to be mounted simultaneously to the shaft, which can be inconvenient in particular when the free space around the counterbalancing mechanism is limited.

In one aspect, the gear wheel comprises a gear rim adapted to be connected to the gear mechanism, wherein the first wheel segment comprises a first set of teeth and the second wheel segment comprises a second set of teeth, and wherein the first set of teeth and the second set of teeth together form the gear rim when the second segment is in an attached state. Thereby, a gear rim comprising teeth is formed by the teeth of the first and second segments such that a complete gear rim is achieved when the second wheel segment is attached to the first wheel segment. In one aspect, the gear wheel comprises a central hole adapted to accommodate the shaft of the counterbalancing mechanism. Thereby, the gear wheel and thus also the tensioning tool is easily and rapidly mounted on and properly connected to the shaft of the counterbalancing mechanism. In one aspect, the fastening means is arranged on the first wheel segment. Thereby, the first wheel segment is connected and affixed to the torsion spring.

In one aspect, the fastening means comprises one pin radially connectable to the torsion spring. One pin is a suitable way of connecting the gear wheel to the torsion spring. A torsion spring of a counterbalancing spring is usually equipped with a winding cone having radial holes and thus one pin is a suitable way to easily and rapidly connect the gear wheel to the torsion spring by inserting the pin in one of the radial holes such that the torsion spring can be rotated and wound when the gear wheel is rotated.

In one aspect, the gear mechanism comprises a worm and a second gear wheel arranged to transmit a rotational movement from the worm to the gear wheel comprising the first and second wheel segments. A worm is a suitable way of transferring a rotational movement to a gear wheel when a high torque is desirable. A second gear wheel transferring the rotational movement from the worm to the gear wheel comprising the first and second segments can further increase the transferred torque.

In one aspect, the gear mechanism is adapted to be rotated by an external drive unit. By use of a drive unit, the necessary human hand force to tension the torsion spring is reduced and substantially eliminated. By having an external drive unit, the tensioning tool is simplified and made less expensive. A standard external drive unit, such as a screw gun or drilling machine can be used. A suitable external drive unit is usually readily available and a screw gun is present at least a standard equipment for a fitter installing an overhead door. In one aspect, the fastening means comprises a distance member adapted to arrange the gear wheel remote from the tensioning spring. Thereby, a distance is achieved between the gear wheel and the torsion spring. This implies that a key that locks the winding cone and the shaft of the counterbalancing mechanism to each other can be mounted while the tensioning tool is mounted on the shaft and connected to the torsion spring, i.e. while the tensioning tool keeps the torsion spring tensioned. Thereby, one must not rely on tightening screws until the key is mounted and the tightening screws may even be eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail with reference to the accompanying drawings, in which:

Figure 1 is a top view of an embodiment of a torsion spring tensioning tool according to the present invention.

Figure 2 is a bottom view of the embodiment of a torsion spring tensioning tool shown in figure 1.

Figure 3 is side view of the embodiment of a torsion spring tensioning tool shown in figures 1 and 2.

Figure 4 is a perspective view of the embodiment of a torsion spring tensioning tool shown in figures 1-3, where a second housing part has been detached. Figure 5 is a perspective view of the embodiment of a torsion spring tensioning tool shown in figures 1-3, where a second housing part has been removed and a gear wheel has been detached.

Figure 6 is a perspective view of the embodiment of a torsion spring tensioning tool shown in figures 1-3, where a second housing part and pieces of the first housing part have been removed to show a gear mechanism.

Figure 7 is a perspective view of a gear wheel of the embodiment of a torsion spring tensioning tool shown in figures 1-3, where a second wheel segment has been detached from a first wheel segment.

Figure 8 is a perspective view of a gear wheel of the embodiment of a torsion spring tensioning tool shown in figures 1-3, where a second wheel segment is attached to a first wheel segment. DETAILED DESCRIPTION

A torsion spring tensioning tool for tensioning a torsion spring of a counterbalancing mechanism of an overhead door is shown in figures 1-3 and details thereof are shown in figures 4-8.

The torsion spring tensioning tool (10) comprises a gear wheel (60). The gear wheel (60) comprises a gear rim (61, 62). The gear rim (61, 62) is arranged along the circumference of the gear wheel (60). The gear rim (61, 62) comprises external teeth (77, 78). The external teeth (77, 78) are directed radially outwards. The gear wheel (60) comprises a first wheel segment (71) and a second wheel segment (72). The first wheel segment (71) and the second wheel segment (72) together form a complete gear wheel (60). The gear wheel (60) is thus divided into the first wheel segment (71) and the second wheel segment (72). As an alternative, the gear wheel may comprise further wheel segments and then all the wheel segments together form a complete gear wheel. Each wheel segment (71, 72) can be seen as a piece of a pie. The first wheel segment (71) is preferably larger than the second wheel segment (72) and then the first wheel segment (71) may be seen as a major wheel segment (71) and the second wheel segment (72) may be seen as a minor wheel segment (72).

By a wheel segment as used herein is meant an element being a part of a circle. A wheel segment is preferably substantially formed as a piece of a pie. A wheel segment may substantially have the shape of a circular sector.

The first and second wheel segments (71, 72) are releasable form each other. The second wheel segment (72) is detachable from the first wheel segment (71). The second wheel segment (72) is in an attached state when the second wheel segment (72) is attached to the first wheel segment (71), i.e. when the first wheel segment (71) and the second wheel segment (72) are attached to each other. The second wheel segment (72) is in a detached state when the second wheel segment (72) is detached from the first wheel segment (71), i.e. when the first wheel segment (71) and the second wheel segment (72) are separated from each other. The first wheel segment (71) comprises a first set of teeth (77) and the second wheel segment (72) comprises a second set of teeth (78). The first set of teeth (77) is arranged along a first arc (79) of the first wheel segment (71) and the second set of teeth (78) is arranged along a second arc (80) of the second wheel segment (72). The teeth (77, 78) of the first and second set of teeth (77, 78) are external teeth. The teeth (77, 78) of the first and second set of teeth (77, 78) are directed radially outwards. The first set of teeth (77) and the second set of teeth (78) together form the gear rim (61, 62) when the second segment (72) is in the attached state.

The gear wheel (60) is adapted to be mounted on a shaft of the counterbalancing mechanism. The gear wheel (60) comprises a central hole (63). The central hole (63) is arranged in the center of the gear wheel (60). The central hole (63) is adapted to accommodate the shaft of the counterbalancing mechanism. The central hole (63) is preferably circular. When the second wheel segment (72) is detached from the first wheel segment (71), the first wheel segment (72) is mountable on the shaft of the counterbalancing mechanism, although the ends of the shaft are attached to e.g. a wall of the building in which the overhead door is installed. When the second wheel segment (72) is in the detached state, the first wheel segment (71) is radially mountable on the shaft of the counterbalancing mechanism. When the second wheel segment (72) is in the detached state, the central hole (63) is accessible from the circumferential periphery of the gear wheel (60). The central hole (63) has a diameter that is at least as large as a diameter of the shaft of the counterbalancing

mechanism.

The first wheel segment (71) can be described as having a through slot (81) extending from the circumference of the gear wheel (60) to the center of the gear wheel (60). The through slot (81) connects the central hole (63) with the surroundings. The through slot (81) extends from the circumference of the gear wheel (60) to the central hole (63). The through slot (81) is devised such that a shaft of the counterbalancing mechanism can be conveyed through the through slot (81) and into the central hole (63). The second wheel segment (72) is adapted to the through slot (81). The second wheel segment (72) mates with the through slot (81) of the first wheel segment (71). The through slot (81) can be seen as a cutout comprised in the first wheel segment (71). The through slot (81) has a width that is at least as large as a diameter of the shaft of the counterbalancing mechanism. In the attached state, the second wheel segment (72) interacts with the first wheel segment (71) such that the second wheel segment (72) is obstructed from moving radially outwards. The second wheel segment (72) is thereby fixed radially outwards in relation to the first wheel segment (71). The first wheel segment (71) has a first radial profile (73) and the second wheel segment (72) has a second radial profile (74). The second radial profile (74) corresponds to the first radial profile (73) such that the second wheel segment (72) is obstructed from moving radially outwards. The through slot (81) has the first radial profile (73). One of the first radial profile (73) and the second radial profile (74) comprises a tongue (75) and the other of the first radial profile (73) and the second radial profile (74) comprises a groove (76) and thereby a tongue-and-groove interaction is achieved between the first and second wheel segments (71, 72). The first radial profile (73) comprises a first shoulder (83) and the second radial profile (74) comprises a second shoulder (84). The second shoulder (84) is adapted to mate with the first shoulder (83) such that the second wheel segment (72) is obstructed from moving radially outwards when the second wheel segment (72) is in the attached state. The second shoulder (84) abuts the first shoulder (83). The first shoulder (83) is directed substantially radially inwards and the second shoulder (84) is directed substantially radially outwards.

In the attached state, the second wheel segment (72) interacts with the first wheel segment (71) such that the second wheel segment (72) is obstructed from moving radially inwards. The second wheel segment (72) is thereby fixed radially inwards in relation to the first wheel segment (71). The first profile (73) has a first profile section (85) that is tapering radially inwards. Thereby, the second wheel segment (72) is obstructed from moving radially inwards. The second profile (74) has a second profile section (86) that also is tapering inwards and mates with the first profile section (85).

The gear wheel (60) comprises a fastening means (91) adapted to be connected to the torsion spring of the counterbalancing mechanism. The fastening means (91) is adapted to be connected to a winding cone, which is connected to the torsion spring. The fastening means (91) comprises a pin (92) that is radially connectable to the torsion spring. The pin (92) is radially connectable to a winding cone, which is connected to the torsion spring. The pin (92) is radially insertable into a radial hole in the winding cone. A winding cone usually comprises several radial holes, commonly four radial holes. The pin (92) is radially insertable in any one of the radial holes of the winding cone. The fastening means (91), such as the pin (92), is arranged on the first wheel segment (71). In operation, the fastening means (91) transmits a rotational movement from the gear wheel (60) to the torsion spring.

The fastening means (91) comprises a distance member (93) adapted to arrange the gear wheel (60) remote from the torsion spring. The distance member (93) is also adapted to arrange the gear wheel (60) remote from the winding cone of the torsion spring. Thereby, the gear wheel (60) is arranged remote from the torsion spring such that there is a distance between the gear wheel (60) and the torsion spring as well as the winding cone of the torsion spring. The distance between the gear wheel (60) and the torsion spring as well as the winding cone of the torsion spring enables mounting of a key on the shaft, which key rotationally locks the winding cone on the shaft. The key is insertable into a key groove formed in the shaft of the counterbalancing mechanism and a key groove formed in the winding cone. The pin (92) is connected to the distance member (93) such that the pin (92) is arranged remote from the gear wheel (60). The distance member (93) extends axially from the gear wheel (60). The pin (92) extends radially from the distance member (93). The pin (92) extends radially from a distal end of the distance member (93), which distal end is opposite to a proximal end attached to the gear wheel. The distance member (93) is an elongated distance member (93). The distance member (93) and the pin (92) together have an L-shape. Thereby, the fastening means (91) can also be described to have an L-shape.

The second wheel segment (72) is axially detachable from the first wheel segment (71).

Thereby, the second wheel segment (72) is detachable from the first wheel segment (71) by an axial movement of the second wheel segment (72) in relation to the first wheel segment (71).

When the first wheel segment (71) is mounted on the shaft of the counterbalancing mechanism and the fastening means (91) is connected to the torsion spring, the second wheel segment (72) is axially detachable from the first wheel segment (71), i.e. the second wheel segment (72) is axially detachable from the attached state to the detached state. Thus, the second wheel segment (72) is adapted to be axially inserted into the through slot (81) and axially removed from the through slot (81). The second wheel segment (72) is detachable in a single direction, i.e. axially. The second wheel segment (72) is only axially detachable from the first wheel segment. The fastening means (91), such as the radially extending pin (92), is located on the first wheel segment (71) and thus the second wheel segment (72) is axially removable. No radial movement of the second wheel segment (72) is necessary to release the second wheel segment (72).

The torsion spring tensioning tool (10) comprises a housing (20). The gear wheel (60) is rotatably arranged in the housing (20). The housing (20) encloses the circumferential periphery of the gear wheel (60). The housing (20) is adapted to axially lock the second wheel segment (72) in relation to the first wheel segment (71). The housing (20) locks the second wheel segment (72) in relation to the first wheel segment (71) during rotation of the gear wheel (60). The housing (20) comprises a flange (23, 24) arranged along the circumference of the gear wheel (60). The flange (23, 24) axially locks the first wheel segment (71) and the second wheel segment (72). The flange (23, 24) comprises a first lip (25, 26) arranged on one axial side of the gear wheel (60) and a second lip (27) arranged on the other axial side of the gear wheel (60).

The housing (20) comprises a first housing part (21) and a second housing part (22). The first housing part (21) and the second housing part (32) are movable in relation to each other such that the gear wheel (60) is detachable form the housing (20). The first housing part (21) and the second housing part (22) are movable in relation to each other such that the housing (20) is opened. Thereby, access to the interior of the housing (20) is achieved. The second housing part (22) is detachable from the first housing part (21). The second housing part (22) is shaped as a circle arc. The housing (20) comprises a handle (28). The handle (28) facilitates mounting of the tensioning tool on the shaft of the counterbalancing mechanism and operation of the tensioning tool since the housing can easily be moved by hand during mounting and easily be kept by hand during operation. The first housing part (21) comprises the handle (28).

The torsion spring tensioning tool (10) comprises a gear mechanism (40). The gear mechanism (40) rotates the gear wheel (60) during operation of the tensioning tool (10). Since the gear wheel (60) comprises the fastening means (91), which in operation is connected to the torsion spring of the counterbalancing mechanism and transmits a rotational movement from the gear wheel (60) to the torsion spring, the torsion spring is wound when the gear wheel (60) is rotated. Depending on the direction of the rotation of the gear wheel (60), the torsion spring is either wound up and thereby tensioned or unwound and thereby relaxed, the latter implying that the tension of the torsion spring is reduced.

The gear mechanism (40) comprises a worm (41) which is connected to the gear wheel (60). Thereby, a worm gear is formed. The gear mechanism (40) comprises a second gear wheel (42) arranged between the worm (41) and the gear wheel (60) comprising the first and second wheel segments (71, 72). The second gear wheel (42) transmits a rotational movement from the worm (41) to the gear wheel (60) comprising the first and second wheel segments (71, 72). The purpose of the second gear wheel (42) is to further increase the torque. The second gear wheel (42) should therefore have a smaller number of teeth than the gear wheel (60) comprising the first and second wheel segments (71, 72).

The gear mechanism (40) is arranged in the housing (20). The gear mechanism (40) is arranged in the first housing part (21).

The gear mechanism (40) is adapted to be rotated by an external drive unit. An external drive unit is connectable to the worm (41). Thereby, the worm (41) is driven by the external drive unit. The worm (41) is rotated by the external drive unit. The worm (41) rotates the second gear wheel (42). The second gear wheel (42) rotates the gear wheel (60) comprising the first and second wheel segments (71, 72). The gear wheel (60) comprising the first and second wheel segments (71, 72) is connected to the torsion spring. Thereby, the torsion spring is tensioned by the external drive unit. The external drive unit may be a screw gun or a drilling machine. The gear mechanism (40), and in particular the worm (41), is adapted to be connected to a screw gun or drilling machine.

A counterbalancing mechanism is usully used in overhead sectional doors. Thus, the overhead door may be an overhead sectional door.

The mounting, operation and removal of the torsion spring tensioning tool (10) can be described as follows.

The tensioning tool (10) may be mounted on a shaft of a counterbalancing mechanism and connected to a torsion spring in the following way. The second housing part (22) is detached and separated from the first housing part (21). The gear wheel (60) is detached and removed from the first housing part (21). The second wheel segment (72) is axially detached and separated from the first wheel segment (71). The first wheel segment (71) is mounted on the shaft of the counterbalancing mechanism by a radial motion such that the shaft is guided through the through slot (81) and to the central hole (63) and the pin (92) on the first wheel segment (71) is inserted into a radial hole in the winding cone of the counterbalancing mechanism. The second wheel segment (72) is axially attached to the second wheel segment

(72) by axially inserting the second wheel segment (72) into the through slot (81) such that the second radial profile (74) of the second wheel segment (72) mates with the first radial profile

(73) of the first wheel segment (71). The first housing part (21) is moved such that the gear wheel (60) is inserted into the first housing part (21). The second housing part (22) is attached to the first housing part (21). If the space is limited, e.g. if the counterbalancing mechanism is located close to a wall or ceiling, the first wheel segment (71) is preferably oriented such that the through slot (81) is directed substantially towards the wall, the ceiling, or a corner formed where a wall meets a ceiling. Since the second wheel segment (72) is axially attached to the first wheel segment (72), no extra radial space is required to attach the second wheel segment (72) to the first wheel segment (71). The second wheel segment (72) has no pin for connection to a winding cone and therefore only axial movement is necessary to install the second wheel segment (72). The first housing part (21), which comprises the handle (28) and in which the gear mechanism (40) is arranged, is preferably oriented such that the handle (28) is directed substantially away from the wall, the ceiling, or a corner formed where a wall meets a ceiling. The smaller second housing part (22) that is shaped as a circle arc is easily moved into a position close to the wall, the ceiling, or the corner and attached to the first housing part (21), even when the space is limited.

The tension tool (10) may be operated to tension the torsion spring of the counterbalancing mechanism in the following way. A screw gun is connected to the worm (41) such that rotation of the screw gun rotates the worm (41). The worm (41) rotates the second gear wheel (42) at a lower rotational speed and the transferred torque is significantly higher than the torque of the screw gun. The second gear wheel (42) rotates the gear wheel (60) comprising the first and second wheel segment (71, 72) at an even lower rotational speed and the transferred torque is even higher. The rotation of the gear wheel (60) comprising the first and second segment (71, 72) is transferred to the winding cone via the pin (92) arranged on the first wheel segment (71). Thereby, the torsion spring is wound. To tension the torsion spring, the direction of rotation of the screw gun is chosen such that the torsion spring is wound up.

When suitable tension of the torsion spring has been achieved, the winding cone is

rotationally locked to the shaft of the counterbalancing mechanism by tightening tightening screws arranged in the winding cone and engaging the shaft and/or by inserting a key in a key groove formed in the shaft and the winding cone.

The tensioning tool (10) can be removed from the counterbalancing mechanism in the following way. The second housing part (22) is detached and separated from the first housing part (21). The first housing part (21) is removed such that the gear wheel (60) is detached from the first housing part (21). The second wheel segment (72) is axially detached from the first wheel segment (71) by axially moving the second wheel segment (72) out from the through slot (81) of the first wheel segment (71). The second wheel segment (72) is thereby axially detached and separated from the first wheel segment (71). The first wheel segment (71) is removed from the shaft of the counterbalancing mechanism by a radial motion such that the shaft is guided through the through slot (81) and the pin (92) on the first wheel segment (71) is pulled out from the radial hole in the winding cone of the counterbalancing mechanism. If the space is limited, e.g. if the counterbalancing mechanism is located close to a wall or ceiling, the rotation of the gear wheel (60) is preferably stopped such that the through slot (81) of the first wheel segment (71) is directed substantially towards the wall, the ceiling, or a corner formed where a wall meets a ceiling. Thereby, the first wheel segment (71) is easily removable from the shaft.

It is easily realized that the tensioning tool (10) can be used to relax the tension of the torsion spring by operating the screw gun in the opposite direction.

The foregoing has described the principles, preferred embodiments and aspects and modes of operation of the present invention. However, the description should be regarded as illustrative rather than restrictive, and the invention should not be limited to the particular embodiments and aspects discussed above. The different features of the various embodiments and aspects of the invention can be combined in other combinations than those explicitly described. It should therefore be appreciated that variations may be made in those embodiments and aspects by those skilled in the art without departing from the scope of the present invention as defined by the following claims.