Description

The present invention relates to a device for applying a rotary force having a predefinable maximum torque onto a fastening element according to the preamble of claim 1, as well as to the use of such a device according to the preamble of claim 14.

Torque-limiting instruments are typically used for fastening screws or other rotatable fastening elements with a maximum applied torque. They can be used in many different technical fields, amongst others, within the medical-technical field.

US 2016/0354581 Al describes a medical use torque-limiting driver that disengages at a predetermined torque limit. This driver comprises a shaft made of a plastic material. At the same time, the driver comprises a spring made from metal for applying an axial pretensioning.

US 2015/0202018 Al describes a torque-limiting instrument having a shaft that can be made of the plastic material. The torque-limiting instrument further comprises one or more biasing members for applying a pretensioning to a latching mechanism.

US 2015/0148829 Al describes an apparatus for operating on tissue with the help of ultrasonic vibrations, wherein the apparatus comprises a torque-limiting mechanism. The torque-limiting mechanism, in turn, comprises resilient members that can be put into contact with or can be brought out of contact with a moving surface of a handle. US 2014/0276893 Al describes a torque-limiting instrument comprising a torque transfer member that can cyclically iterate between a first configuration and a second configuration. In the second configuration, either a handle or the torque transfer member is deformed such that the handle is decoupled from the torque transfer member and can rotate relatively to the torque transfer member.

US 2017/0105813 Al describes a rotatable fastening device with an integral torque limiter. The torque limiter may comprise an element with three springy arms that are located in an equal distribution around a central axis of the element. The springy arms can engage with or disengage from a latching mechanism of handle of the device.

US 2010/0275744 Al describes a torque wrench for use with an implantable medical device, wherein the torque wrench comprises an element with flexible fingers made from a polymeric material. This element serves as a torque-transmitting and torque-limiting element.

Thus, there exist many different mechanisms to transfer a maximum torque from a handle to a tool-holding component of a torque wrench. According to some of the solutions known from prior art, the torque is exclusively adjusted by the geometry and/or stiffness of individual latching hooks and thus of the resistance force of a radially oriented toothing between these latching hooks and corresponding latching elements within a handle.

In such a case, even small deviations of the dimensions of the individual components of the torque wrench can have a tremendous influence on the maximum transferable torque. Thus, particular care must be taken when manufacturing such a torque wrench in order to avoid an undesired adjustment of the maximum transferable torque.

Other torque wrenches known from prior art use metallic springs that adjust the maximum transferable torque. To give an example, an axial compression spring can act upon an axially oriented toothing and serves for a disengagement of the toothing upon exceeding the spring force. However, the use of metallic springs makes the manufacture of an according torque wrench much more complex and expensive. Furthermore, it has been dealt with metallic abrasion from the metallic spring. This is particularly problematic if the torque wrench is to be used for medical applications.

It is an object of the present invention to provide a torque-limiting instrument that allows a simple and reliable adjustment of the maximum transferable torque and that can be manufactured in a particularly cheap and easy way.

This object is achieved with a device for applying a rotary force having a predefinable maximum torque onto a fasting element having the claim elements of claim 1. Such a device can also be denoted as torque-limiting device. It comprises a handle element, a toolholding element, a force transmission element, and a pretensioning element. The force transmission element serves for transmitting a force applied onto the handle element to the tool-holding element. The pretensioning element serves for applying a pretensioning onto the force transmission element. In this context, the pretensioning applied by the pretensioning element serves for predefining a maximum torque applicable by the holding element. If the applied torque is below the maximum torque, the force transmission element serves for force transmission between the handle element and the tool-holding element. If, however, the applied torque exceeds the maximum torque, the force transmission element no longer transmits the force applied onto the handle element to the tool-holding element. Rather, the force transmission element disengages at least one of the handle element and the tool-holding element in such a case, resulting in an interruption of a force transmission between the handle element and the tool-holding element.

According to an aspect of the present invention, the pretensioning element is made from an elastic polymer. This elastic polymer has a Shore A hardness (being measured according to ASTM D2240) lying in a range of from 30 to 85, in particular of from 35 to 80, in particular of from 40 to 75, in particular of from 45 to 70, in particular of from 50 to 65, in particular of from 55 to 60. Such an elastic polymer having a Shore A hardness in the indicated range is particularly appropriate to apply a pretensioning onto the force transmission element to allow for an adjustment of the maximum torque transferred by the force transmission element in a particularly appropriate range for many applications, in particular for many applications in the medical-technical field. In this context, it should be emphasized that the pretensioning element is an individual part of the torque-limiting device that is separate from the handle element, the tool-holding element and the force transmission element. Therefore, the pretensioning element can also be denoted as additional component of the torque-limiting device.

Due to this pretensioning element, it is not necessary to design the force transmission element or other elements of the torque-limiting device in a sophisticated or complex way, as some of the prior art solutions do. Rather, the additional provision of the pretensioning element allows a simple design of the other components of the torque-limiting device and enables a manufacturing process with high tolerance. Any necessary adjustment of the desired maximum torque transferred by the force transmission element can be easily achieved by choosing a pretensioning element having an appropriate Shore A hardness lying within the above-indicated range.

Expressed in other words, the torque-limiting device allows for a particularly easy compensation of tolerances during the manufacturing process of the torque-limiting device. Thus, the device can be produced with bigger allowed tolerances that can be easily compensated afterwards by choosing a pretensioning element having the required hardness. Consequently, the pretensioning element serves for an exact adjustment of the maximum torque to be transmitted from the handle element to the tool-holding element of the torque-limiting device.

By providing different additional pretensioning elements, one and the same torque-limiting device scaffold (i.e., the torque-limiting device with all components but the pretensioning element) can be used to produce devices for applying a rotary force having a predefinable maximum torque onto a fasting element with different maximum torques. To give an example, a clamping force of a clamping element to fasten a neurostimulation electrode on an electrode fixation sleeve must be much lower than a clamping force of an electrode plug in a header of an implantable pacemaker since the neurostimulation electrode is much more damageable than such an electrode plug. By using a pretensioning element having a Shore A hardness at the lower end of the aboveindicated range results in a torque-limiting device by which the maximum applicable torque onto a clamping element is much lower than in case of a pretensioning element having a Shore A hardness lying at the upper end of the above-indicated range. Therefore, a torque-limiting device with a softer pretensioning element can be particularly well used for fixing a neurostimulation electrode, whereas a torque-limiting device comprising a harder pretensioning element can well be used for clamping an electrode plug of an implantable pacemaker. At the same time, the remainder of the torque-limiting device (besides the pretensioning element) is completely the same. Thus, the additional pretensioning element allows the production of a universally usable torque-limiting device in a particularly easy manner.

By using an elastic polymer for forming the pretensioning element, the torque-limiting device can be produced in a much cheaper manner than torque-limiting devices known from prior art making use of metallic springs. Furthermore, no metallic abrasion will occur within the torque-limiting device. This reduces the risk of contaminations of a medical device being manufactured by using the presently claimed and described torque-limiting device.

In an embodiment, the pretensioning applied by the pretensioning element onto the force transmission element is radially oriented with respect to an axis running along a longitudinal direction of extension of the device. To give an example, the pretensioning element can be designed as a cylindrical body, wherein latching elements of the force transmission element are arranged around it. Then, the pretensioning element will push the latching elements radially outwards towards an inner wall of the handle element. The higher the force applied by the pretensioning element, the higher is the maximum transferable torque between the handle element and the force transmission element.

In an embodiment, the pretensioning applied by the pretensioning element onto the force transmission element is axially oriented with respect to an axis running along a longitudinal direction of extension of the device. Such axially oriented pretensioning force can be chosen alternatively or in addition to the previously explained radially oriented pretensioning force. To give an example, the axially oriented pretensioning can press onto a latching disk being mounted in a torque-proof manner within the handle element. Latching elements of the latching disk can then engage the tool-holding element, as long as the applied force does not exceed the pretensioning of the pretensioning element. If the applied force exceeds the pretensioning, the latching elements will disengage from the tool-holding element. This results in an interruption of a force transmission between the handle element and the tool-holding element.

In an embodiment, the force transmission element forms an integral part of the toolholding element. In such a case, no relative movement between the force transmission element and the tool-holding element is possible. Rather, a disengagement between the force transmission element and the handle element is necessary in order to interrupt the force transmission between the handle element and the tool-holding element. Such an arrangement is particularly appropriate in case of a radially acting pretensioning force of the pretensioning element.

In an alternative embodiment, the force transmission element is a separate part being arranged within the handle element in a torque-proof manner with respect to the handle element. Then, an axial movement (along an axis running in a longitudinal direction of extension of the device) of the force transmission element is still possible. Such axial movement is, however, limited by the pretensioning element applying an axially oriented force onto the force transmission element.

In an embodiment, the force transmission element comprises latching elements that engage the handle element or the tool-holding element for achieving a force transmission between the handle element and the tool-holding element. If the force transmission is to be interrupted, disengagement between the latching elements on the one hand and the handle element or the tool-holding element, respectively, on the other hand is required. The geometry of the latching elements together with counterparts into which the latching elements engage is co-decisive for the maximum transferable force between the handle element and the tool-holding element. The latching elements can, e.g., have the shape of latching hooks. In an embodiment, the latching elements are oriented in the same direction like a pretensioning applied by the pretensioning element onto the force transmission element. Then, the pretensioning applied by the pretensioning element directly acts upon the latching elements in their preferred direction of engagement with the respective engaging surface of the handle element or of the tool-holding element. This will result in a particularly appropriate transmission of the pretensioning into a regulation of the strength of interaction between the latching elements and their corresponding engaging surface.

In an embodiment, the latching elements are radially oriented with respect to an axis running along a longitudinal direction of extension of the device. At the same time, the latching elements are engaging an inner wall of the handle element in this embodiment. A pretensioning will then also act in a radial direction (i.e., it will press the latching elements radially against the inner wall of the handle element).

In an embodiment, the latching elements are axially oriented with respect to an axis running along a longitudinal direction of extension of the device. At the same time, the latching elements are engaging the tool-holding element in this embodiment. Then, an axially oriented pretensioning force of the pretensioning element will press the latching elements against an engaging surface of the tool-holding element.

In an embodiment, the elastic polymer is chosen from the group consisting of rubber, thermoplastic elastomers, and silicone (polysiloxane). Generally, any kind of thermoplastic elastomer is appropriate to be used as pretensioning element. Particularly appropriate thermoplastic elastomers belong to the groups of styrenic block copolymers (TPS, TPE-s), thermoplastic polyolefmelastomers (TPO, TPE-o), thermoplastic vulcanizates (TPV, TPE- v), thermoplastic polyurethanes (TPU), thermoplastic copolyesters (TPC, TPE-E), and thermoplastic polyamides (TP A, TPE-A).

Depending on the required design according to the geometry of the force transmission element and/or an interior of the handle element, the elastic polymer can be brought into any desired shape required for the pretensioning element. In an embodiment, the pretensioning element is removably housed within the handle element and/or within the force transmission element. In such a case, it can be replaced by a user of the torque-limiting device in case that the maximum transferable torque shall be adjusted by the user. Thus, such an arrangement makes possible a multi-purpose application of the torque-limiting device in a particularly simple manner.

In an embodiment, the torque-limiting device can be offered in form of a set comprising the torque-limiting device together with a plurality of different pretensioning elements having an individual Shore A hardness. Then, the torque transmitting properties of the torque-limiting device can be particularly easy adjusted by replacing one of the pretensioning elements by any of the other pretensioning elements.

In an embodiment, the maximum torque applicable by the tool-holding element lies in a range of from 1 N to 100 N, in particular of from 2 N to 90 N, in particular from 3 N to 80 N, in particular of from 4 N to 70 N, in particular of from 5 N to 60 N, in particular of from 6 N to 50 N, in particular of from 7 N to 40 N, in particular of from 8 N to 30 N, in particular from 9 N to 20 N, in particular of from 10 N to 15 N, in particular of from U N to 14 N, in particular of from 12 N to 13 N. Such a maximum torque is particularly appropriate for fastening elements of medical devices that are often more damageable than other mechanic components of devices from other technical fields.

In an embodiment, the device comprises a tool for engaging a fastening element. This tool is present within the tool-holding element in a torque-proof manner with respect to the tool-holding element. Thus, any torque applied by the tool-holding element will be directly transferred to the tool.

In an embodiment, the tool is irremovably connected with the tool-holding element. This excludes the risk of choosing a tool being not appropriate for engaging a specific fastening element. Rather, the user of the torque-limiting device will not have to worry about choosing the correct tool for the intended purpose in this embodiment. In another embodiment, the tool can be removed from the tool-holding element to be replaced against another tool. This offers a wider range of applications of the torquelimiting device.

In an aspect, the present invention relates to the use of a device according to the preceding explanations for fastening a fastening element of a medical device. As explained above, the torque-limiting device is particularly designed for manipulating such medical devices.

In an embodiment, the medical device is an implantable medical device for stimulating a human or animal heart. An implantable pacemaker or an implantable cardioverter/defibrillator is a particularly appropriate device for stimulating a human or animal heart. The torque-limiting device may be used for connecting an electrode to the housing of such medical device.

All embodiments of the described torque-limiting device can be combined in any desired way and can be transferred either individually or in any arbitrary combination to the described use. Likewise, all embodiments of the described use can be combined in any desired way and can be transferred either individually or in any desired manner to the described torque-limiting device.

Further details of aspects of the present invention will be explained in the following making reference to exemplary embodiments and accompanying Figures. In the Figures:

Figure 1 A shows a first embodiment of a torque-limiting device in a partially cut view;

Figure IB shows a perspective view on a part of the torque-limiting device of Figure 1A;

Figure 1C shows another partially cut perspective view of the force limiting device of Figure 1A; and

Figure 2 shows a partially cut view of a second embodiment of a torque-limiting device. Figure 1 A shows a partially cut view on a torque wrench 1 serving as device for applying a rotary force having a predefinable maximum torque, or torque-limiting device. The torque wrench 1 comprises a handle 2 serving as handle element. Furthermore, it comprises a tool holder 3 serving as tool-holding element. The tool holder 3 holds a tool 4 that is intended to rotate a screw with a maximum applicable torque. The torque wrench 1 extends along an axis L running in a longitudinal direction of extension.

To limit the torque exerted by the tool 4, the tool holder 3 further comprises latching fingers 5 that serve as force transmission elements. The latching fingers 5 comprise terminally arranged latching hooks 6 that press against an inner wall 7 of the handle 2. For this purpose, the inner wall 7 comprises a plurality of recesses into which the latching hooks 6 can engage. If the force applied onto the handle 2 is too high, the latching hooks 6 disengage from the recesses of the inner wall 7 of the handle 2 so that no force is any longer transferred to the latching fingers 5 and thus to the tool holder 3 or the tool 4, respectively.

The latching fingers 5 form an integral part of the tool holder 3. The tool holder 3 with its latching fingers and terminally arranged latching hooks 6 can be manufactured, e.g., by injection molding.

In order to achieve sufficiently high and well-defined pretensioning of the latching hooks 6 against the inner surface 7 of the handle 2, an elastic component 8 is placed in a central space surrounded by the latching fingers 5. The elastic component 8 serves as pretensioning element and exerts a pretensioning on the latching hooks 6 acting radially to the axis L. Depending on the hardness of the elastic component 8, the pretensioning can be adjusted to the respective needs.

For manufacturing the torque wrench 1, the elastic component 8 can be simply inserted into the central space surrounded by the latching fingers 5. Typically, it will be held in place due to a pressure force exerted between the elastic component 8 and the latching fingers 5. If desired, the elastic component 8 can also be removed and replaced by a different elastic component having a different hardness and thus applying different pretensioning onto the latching fingers 5.

Figure IB shows a perspective view onto the torque wrench 1 of figure 1A, however, without the handle 2 shown in Figure 1A. In this and in all following Figures, similar elements will be denoted with the same numeral references.

In the depiction of Figure IB, it can particularly well be seen that the tool holder 3 and the latching fingers 5 with their latching hooks 6 form a single part. In contrast, the elastic component 8 is a separate element inserted into a receiving space defined by the latching fingers 5.

Figure 1C shows a partially cut view of the torque wrench 1 of Figure 1A onto a backside of the torque wrench 1. Here, the elastic component 8 received between the latching fingers 5 can particularly well be seen. The elastic component 8 has a generally cylindrical shape. This allows a particularly easy manufacturing (e.g., in form of a polymeric strand). The harder the elastic component 8, the higher is the maximum torque that can be transferred from the handle 2 by rotating the handle 2 about the axis L.

Figure 2 shows another embodiment of a torque wrench 1. This torque wrench 1 comprises - like the torque wrench 1 shown in Figures 1 A to 1C - also a handle 2, a tool holder 3 and a tool 4 housed by the tool holder 3. In contrast to the embodiment shown in Figures 1A to 1C, a latching disk 5 is provided instead of latching fingers. This latching disk 5 does not form an integral part with the tool holder 3. Rather, it is a separate part mounted in a torque-proof manner with respect to and within the handle 2. However, an axial movement of the latching disk 5 is still possible so that latching hooks 6 present on a bottom side of the latching disk 5 can engage an engaging surface 9 of the tool holder 3 and can disengage from this engaging surface 9.

If the latching hooks 6 are engaged with the latching surface 9, a torque applied to the handle 2 will be transmitted to the tool holder 3 and thus to the tool 4. For this purpose, an elastic component 8 exerts an axially oriented pretensioning onto the latching disk 5, i.e., a pretensioning along the axis L running in a longitudinal direction of extension of the torque wrench 1. If the torque applied by the handle 2 exceeds a threshold, the pretensioning force of the elastic component 8 is no longer sufficient to keep the latching hooks 6 in engagement with the engaging surface 9 so that the latching disk 5 slightly compresses the elastic component 8 and moves proximally (i.e. to the right side in Figure 2). Then, turning the handle 2 will no longer have any force transmission effect onto the tool holder 3 or the tool 4. Expressed in other words, the torque-limiting mechanism of the torque wrench 1 is then activated and prevents the application of an undesirable high force by the tool 4.

While the embodiment of Figures 1A to 1C realizes a radial pretensioning of the latching fingers 5 by the elastic component 8, the embodiment shown in Figure 2 makes use of an axial pretensioning of the latching disk 5 against the tool holder 3. However, the final result of a torque-limiting mechanism remains the same.