Background of the invention

[0001] The invention relates to a travel limiter, an arrangement comprising one and to a power transmission device that may be used to assist in machining inner surfaces of pipes, for example.

[0002] Fl Patent 123198 discloses a power transmission device comprising a wire rope and a sheath at least partly surrounding the wire rope, a drum arranged to be rotatabie, and a motor connected to the leading end of the wire rope for rotating the wire rope. Inside the drum, there is a motor attached to the drum or to its bottom plate so that the motor rotates with the drum. The sheath lowermost in the drum is turned inside the drum and the leading end of the wire rope is arranged to be fastened to the motor.

[0003] A problem with the above-described arrangement is that the sheath slowly moves towards the free end of the wire rope, i.e. the end to which a tool is to be fastened. Therefore the sheath must be shortened at its open end from time to time and thus the sheath at the motor end escapes further away from the motor, exposing the wire rope. It has been observed that an exposed wire rope only sustains a fraction of the torque that a wire rope covered by a sheath would sustain.

Brief description of the invention

[0004] An object of the invention is thus to provide a device and an arrangement that allow the aforementioned problems to be solved. The object of the invention is achieved by a device and an arrangement characterised by what is disclosed in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.

[0005] The invention is based on the use of a travel limiter in connection with the wire rope and the sheath for preventing the sheath from escaping and the wire rope at the motor end from being exposed. The travel limiter is a tubular device with threads, for example, on the inner surface at one end thereof for fastening the travel limiter to the sheath. The tubular inner part of the travel limiter narrows so that the sheath only fits into the threaded end, the exposed wire rope exiting from the opposite end to the motor. The travel limiter has a collar which, together with a guide, prevents the sheath from escaping.

[0006] An advantage of the device and arrangement of the invention is that the sheath stays in place in relation to both the wire rope and the motor and thus a high torque may also be applied as the device becomes older.

Brief description of the drawings

[0007] The invention is now described in closer detail in connection with the preferred embodiments and with reference to the accompanying drawings, in which:

Figure 1 shows a prior art power transmission device with no travel limiter arrangement;

Figure 2 shows a travel limiter according to an embodiment of the invention;

Figure 3 shows a travel limiter arrangement according to an embodiment of the invention; and

Figure 4 shows a power transmission device according to an embodiment of the invention, the device comprising a travel limiter arrangement.

Detailed description of the invention

[0008] Figure 1 shows a prior art power transmission device seen from above. The device has a body 134 and, arranged in connection with it, a drum 131 that is rotatable on a vertical shaft. The body is provided with a carry handle 130 that makes the device easy to lift and move. The body is also provided with a power switch 138 for switching the power transmission on and off.

[0009] Power transmission takes place by means of a power transmission device 10, hereinafter referred to as a wire rope. Except for its free ends, the wire rope 110 is inside a plastic sheath 112 where it is able to rotate when necessary. The trailing end of the wire rope is provided with means for fastening a tool to the wire rope. The wire rope 10 travels through a guide 20, which is a tube or a loop, for example. When the wire rope in the sheath is being pushed inward, the guide 120 guides the wire rope onto the drum and, when the wire rope is pulled outward, unwinds it from the drum. Because of the stiffness of the rotatable drum 131 and the wire rope 110, even long stretches of the wire rope are easy to feed onto the drum and to unwind from the drum by handling only the wire rope 110 or its sheath 112, for example by pulling the sheath, which unwinds the wire rope from the drum.

[0010] The inner part of the drum 131 is provided with a motor 1 0 fastened either directly to the drum or to its bottom plate by fastening means 142 so that the motor rotates with the drum. The sheath that is lowermost on the drum is turned inside the drum and the leading end 111 of the wire rope is arranged to be fastened to the motor 140. The motor rotates the wire rope 110, which rotates in the sheath 112, the motor 140 thus causing also a tool to be fastened to the trailing end of the wire rope 0 to rotate.

[0011] When the device is being used, the wire rope 110 is pulled from the drum 131 by pulling the sheath 1 2, the wire rope rotating at the same time in the sheath. When the sheath 112 is being pulled, it moves a little closer to the free end of the wire rope, i.e. further away from the motor. Pushing of the wire rope by the sheath back onto the drum 131 does not move the sheath 12 back in a corresponding manner, so when the pulling is repeated often enough, the sheath 2 moves clearly and exposes the wire rope 110 at the vicinity of the motor for a distance of several centimeters or tens of centimeters. Measurements showed a case in which a wire rope exposed for a short distance at the motor end remained unbroken for only one quarter of the torque a wire rope surrounded by a sheath did.

[0012] Figure 2 shows a travel limiter according to an embodiment of the invention. The tubular travel limiter comprises a sheath end 10, a wire rope end 30 at an opposite end in relation to the former, and a collar 20 between the ends. The outer diameter of the collar 20 is different from the outer diameter of the sheath end 10 and from that of the wire rope end 30. The outer diameter of the collar 20 is preferably greater than the outer diameters of the ends 10, 30. According to an embodiment, the outer diameter of the sheath end 10 is greater than the outer diameter of the wire rope end 30, and the outer diameter of the collar 20 is greater than the outer diameter of the sheath end 10. The collar 20 may have a cross-section in the shape of a ring or a nut, for example. In the embodiment of Figure 2 the collar 20 has bevels 22 on opposite sides thereof to allow the travel limiter to be rotated by grabbing the bevels 22 of the collar 20 with a fork wrench or an adjustable wrench, for example.

[0013] The sheath end 10 of the travel limiter is provided with means for fastening the travel limiter to the sheath 112. The inner surface of the sheath end 10 is preferably provided with threads 12 that allow the travel limiter to be screwed to the end of the sheath 112. The travel limiter may be pushed, with the sheath end 10 first, onto a wire rope 110 from which the sheath 112 has been partly peeled off, the travel limiter being then screwed to the end of the sheath 112 whereby the wire rope 110 travels through the travel limiter and comes out from the wire rope end 30. The travel limiter has an inner part 24 that is tubular and preferably consists of two portions of different inner diameters. The inner diameter of the sheath end 10 of the travel limiter is preferably greater than the inner diameter of the wire rope end 30. The inner diameter of the sheath end 10 preferably corresponds substantially to the outer diameter of the sheath 1 2 to allow the travel limiter to be fastened to the outer surface of the sheath 1 2. Since the inner diameter of the travel limiter is smaller at the wire rope end 30 than its inner diameter at the sheath end 10, the travel limiter may be fastened to the sheath 112 by screwing until the sheath meets a narrowing of the inner diameter, i.e. a shoulder, in the travel limiter. The inner diameter of the wire rope end 30 of the travel limiter is preferably about the size of the outer diameter of the wire rope 110, preferably slightly greater than the outer diameter of the wire rope, so that the travel limiter is easier to fit to the wire roper and the wire rope is able to freely rotate inside the travel limiter. According to an embodiment, the tubular inner part 24 of the travel limiter comprises a shoulder at which the inner part 24 narrows so that the sheath 112 only fits into the threaded sheath end 10 and the exposed wire rope 110 exits from the opposite wire rope end 30 to an angle gear 42.

[0014] The travel limiter is preferably made of metal, such as aluminium, magnesium, iron, steel or a mixture of these. According to an embodiment, the travel limiter is of a ceramic material or polymer. The travel limiter may be manufactured by e.g. by turning, moulding or milling. The inner surface of the sheath end 10 may be threaded afterwards by a suitable tool. According to an embodiment, the inner surface of the sheath end 10 is not provided with threads but with wedge-like claws rising from the inner surface towards the wire rope end 30 and allowing the travel limiter to be pushed to the end of the sheath 112 but resisting a movement to the opposite direction, which means that the travel limiter cannot be removed from the end of the sheath 112 without damaging the sheath 112.

[0015] Figure 3 shows a travel limiter arrangement according to an embodiment of the invention. The arrangement comprises a travel limiter and a guide 40. The guide 40 is tubular or in U-shaped and, therefore, when placed against the surface, the groove provided by the guide forms an opening through which the wire rope 110 may travel. The groove or opening provided through the guide 40 may have a width or a diameter that it is at least at one point smaller than the outer diameter of the collar 20 of the travel limiter and thus the travel limiter fastened to the sheath 112 cannot be pulled or pushed entirely through the groove or opening in the guide 40. Preferably, the travel limiter fastened to the sheath 12 may be taken to about half-way the guide 40, where the narrowing groove or opening (hereinafter the groove) of the guide 40 stops the travel limiter.

[0016] The end of the groove of the guide 40 through which the travel limiter may be inserted into the guide is arranged to receive a part of the motor 140, the angle gear 42 or some other means to which the wire rope 110 is arranged to be fastened. In the example of Figure 3, an angle gear 42 is used through which the torque of the motor 140 is transmitted to the wire rope 110. Hence the size of the groove of the guide 40 at one end is such that an end of the angle gear 42 fits into the guide 40. The travel limiter is screwed to the sheath 112, the open wire roper end exiting from the wire rope end 30 of the travel limiter. The wire rope is fastened to the angle gear 42 connected to the motor 140. An end of the angle gear 42 has a recess 44 formed thereto, the diameter of which is preferably slightly greater than the outer diameter of the wire rope end 30 of the travel limiter, the wire rope end thus fitting into the recess but the arrangement does not allow any significant lateral movement. At the bottom of the recess 44 of the angle gear there may be a thrust bearing and, thus, when the angle gear 42 rotates the wire rope and the sheath 112 is being pushed towards the angle gear, the travel limiter meets the thrust bearing at the bottom of the angle gear recess, and the bearing prevents the rotating motion of the inner part of the angle gear and that of the wire rope from being transmitted to the travel limiter. [0017] The guide 40, the angle gear 42 or the motor 140 and the travel limiter are preferably arranged so that the arrangement allows for a small movement of the travel limiter, as shown in Figure 3. When the sheath 112 is being pushed inwards, i.e. towards the angle gear, the movement of the travel limiter stops as the wire rope end 30 meets the bottom of the recess 44 of the angle gear 42 or the thrust bearing residing there. When the sheath 112 is being pulled outward, i.e. away from the angle gear, the movement of the travel limiter stops as the collar 20 meets the narrowing in the groove of the guide 40. The arrangement preferably allows only a small movement, for example 3 to 6 millimetres, of the travel limiter, the arrangement then operating at reasonable mounting and manufacturing tolerances but does not leave the wire rope exposed for a distance that would significantly shorten the torque sustainability of the wire rope.

[0018] Figure 4 shows a power transmission device according to an embodiment of the invention seen from above. The device has a body 134, which is preferably light and strong, made of a metal tube or a suitable plastic, for example. The body is provided with a drum 131 that is rotatable by a vertical shaft. The shaft may be provided with bearings to make the drum rotate more easily. The body is preferably also provided with a carry handle 130 by which the device is easy to lift and move. The device is made so light that one person is able to carry it even on stairs and therefore no extra carriers are needed in addition to the operator of the device. The body is also provided with a power switch 138 for switching the power transmission on and off.

[0019] The power transmission takes place by means of a power transmission device 110, hereinafter referred to as a wire rope. Instead of a wire rope, also some other flexible and yet torsionally rigid means may be used. The wire rope may have a thickness of e.g. 10, 12, 14, 16 or 18 mm, or some other thickness suitable for the purpose. Except for its exposed ends, the wire rope 110 is inside a sheath 112 where it may rotate when necessary. The trailing end of the wire rope may be provided with means for fastening a tool to the wire rope. The sheath 112 is of a flexible material, such as plastic, rubber or a mixture of these. The wire rope 110 may travel through a guide 120, which is a tube or a loop, for example. When the wire rope that is inside the sheath is being pushed inward, the guide 120 guides the wire rope onto the drum and, when the wire rope is being pulled outward, it unwinds the wire rope from the drum. Because of the stiffness of the rotatable drum 131 and the wire rope 10, even long stretches of the wire rope are easy to feed onto the drum and to unwind from the drum by handling nothing but the wire rope 110 and/or its sheath 112.

[0020] The figure shows how the guide 120 guides the wire rope 110 that is in the sheath 112 onto the drum and/or from the drum 131. The difference between the radii of the outer periphery 132 of the drum and the inner periphery 133 of the drum is less than double the diameter of the sheath 12 in use, in which case two sheaths cannot fit side by side but the sheath 112 wound in always sets on top of the previous layer. The inner and outer periphery of the drum is preferably provided with cross rods for keeping the wire rope 110 and the sheath 112 substantially between the inner and the outer periphery. Instead of cross rods, a plate-like solution may also be used. Hence the sheath cannot get stuck on the drum 131 but travels easily onto the drum and is also easy to unwind from the drum. The combination of the wire rope and the sheath is preferably so rigid that when it is pushed onto the drum, the drum rotates as the wire rope is being pushed onto it. This renders the device particularly easy to use and allows the device to be operated single- handedly, even from a distance from the actual body and the drum.

[0021] The inner part of the drum 131 is provided with a motor 140 fastened either directly to the drum or to its bottom plate by fastening means 142 so that the motor rotates with the drum. An angle gear 42 may be used in connection with the motor, and thus the wire rope 1 0 does not need to be bent sharply to connect it to the motor. The sheath that is lowermost on the drum is turned inside the drum and the leading end 111 of the wire rope is arranged to be fastened to the motor 140 by means of the angle gear 42. The leading end of the wire rope may be provided with a safety switch that becomes broken or opens if the torque becomes too great as a result of the wire rope getting stuck, for example. The safety switch prevents additional damage by detaching the wire rope from the motor.

[0022] Figure 3 shows a travel limiter arrangement according to an embodiment of the invention. The arrangement comprises a travel limiter and a guide 40. The guide 40 is tubular or U-shaped and, therefore, when placed against the surface, the groove provided by the guide forms an opening through which the wire rope 110 may travel. The groove or opening provided through the guide 40 may have a width or a diameter that it is at least at one point smaller than the outer diameter of the collar 20 of the travel limiter and thus the travel limiter fastened to the sheath 112 cannot be pulled or pushed entirely through the groove or opening in the guide 40. Preferably, the travel limiter fastened to the sheath 112 may be taken to about half-way the guide 40, where the narrowing groove or opening (hereinafter the groove) of the guide 40 stops the travel limiter.

[0023] The guide 40 is used when the wire rope 110 is fastened to the angle gear 42. One end of the guide 40 is arranged to receive a part of the angle gear 42 to which the wire rope 110 is arranged to be fastened. Hence, at one end the size of the groove of the guide 40 is such that an end of the angle gear 42 fits into the guide 40. The travel limiter is screwed to the sheath 12, the open wire rope end exiting from the wire rope end 30 of the travel limiter. The wire rope is fastened to the angle gear 42 connected to the motor 140. An end of the angle gear 42 has a recess 44 formed thereto, the diameter of which is preferably slightly greater than the outer diameter of the wire rope end 30 of the travel limiter, the wire rope end thus fitting into the recess but the arrangement does not allow any significant lateral movement. At the bottom of the recess 44 of the angle gear there may be a thrust bearing and, thus, when the angle gear 42 rotates the wire rope and the sheath 112 is pushed towards the angle gear, the travel limiter meets the thrust bearing at the bottom of the angle gear recess, the bearing preventing the rotating motion of the inner part of the angle gear and that of the wire rope from being transmitted to the travel limiter.

[0024] The motor is preferably electrically powered and receives it driving power from a battery or the mains, for example. The necessary wiring is brought to the motor through the shaft 136, so the rotation of the drum does not cause a problem. The motor rotates the wire rope 110, which rotates in the sheath 112, the motor 140 thus causing also a tool to be fastened to the trailing end of the wire rope 110 to rotate.

[0025] It is apparent to a person skilled in the art that as technology advances, the basic idea of the invention may be implemented in many different ways. The invention and its embodiments are thus not restricted to the examples described above but may vary within the scope of the claims.