Torque limiting device
Torque limiting devices, tools comprising torque limiting devices and methods for using torque limiting devices are disclosed. In an embodiment, a torque limiting device comprises a first and a second surface disposed in substantially adjacent parallel planar relationship such that within a predetermined torque range the first and second surface rotate together such than a torque applied to the first surface is translated to the second surface. When the torque applied exceeds a certain critical torque, the first and second surfaces slip and therefore the excessive torque is not transferred.
The present invention relates to mechanical devices. Embodiments of the present invention include torque limiting devices, tools comprising torque limiting devices, methods for using torque limiting devices and medical kits comprising torque limiting devices.
BACKGROUNDTools, such as medical tools, may undergo relatively high torque forces. If the torque force is greater than the tool can withstand, the tool may break or fracture. Tool breakage can lead to serious injuries. For example, if a medical tool breaks while still inserted in a patient, the patient may suffer serious injuries. Therefore, it is desirable to design tools such that injury inducing breakage is minimized or eliminated.
In order to avoid injury inducing breakage past tools have been designed to break in a predetermined position when torque forces are greater than the tool can withstand. For example, a groove can be cut such that a predetermined torque causes the tool to break at the groove as the predetermined torque is less than the torque that would cause other portions of the tool to break. Such a design has been used with a form of medical tool referred to as a curette.
Although this prior design may be effective for reducing injuries, it is costly as once the tool is broken it may be useless and therefore replaced. Furthermore, this prior design is inconvenient because when the tool breaks, work must be stopped and restarted with a new tool. In the case of a medical tool, a surgeon must stop surgery, remove the broken portion of medical tool, and insert a new, unbroken tool.
Therefore, it is desirable to provide a device that could minimize injuries from tool breakage resulting from excess torque while allowing the tool to remain functional for repeated use.
SUMMARY OF THE INVENTIONThe present invention provides torque limiting devices, tools, including medical tools, comprising a torque limiting device, methods for using torque limiting devices and medical kits comprising torque limiting devices.
A torque limiting device of the present invention allows a predetermined amount of torque to be applied and then disengages after the predetermined amount of torque has been reached. Torque limiting devices are also referred to in the art by other names, such as, for example, slip clutches, friction torque limiters, overload clutches, torque limiting clutches and the like.
In embodiments, a torque limiting device of the present invention comprises a plurality of substantially planar surfaces disposed in a substantially parallel relationship. At least a first and a second planar surface are resiliently biased against one another such that within a predetermined torque range, rotational movement of the first planar surface results in rotational movement of the second planar surface in the same direction through surface friction. At, or above, a predetermined torque, surface friction is overcome and the first planar surface rotates independently of the second planar surface. In embodiments the first planar surface and second planar surface are resiliently biased through the use of a spring. The spring may comprise a metal and/or a polymer. The spring may comprise a coil spring, a compression spring, an extension spring or a torsion spring.
In some embodiments, the first and second planar surfaces may be disposed in the interior of a housing. The first planar surface may be resiliently biased against the second planar surface through the use of a spring disposed between an interior wall surface of the housing and a side of the first planar surface opposite the side facing the second planar surface.
In some embodiments of a torque limiting device of the present invention, a first planar surface comprises a projection and a second planar surface adjacent to the first planar surface comprises a receptacle. The projection will generally extend in a substantially perpendicular direction from the planar surface. The projection engages the receptacle such that rotation of the first planar surface results in rotation of the second planar surface. When a predetermined torque limit is reached, the projection clears the notch thus forcing the planar surfaces apart. As a result, the second planar surface no longer rotates upon further rotation of the first planar surface. The projection and notch may be realigned and reengaged to permit further rotation.
Projections may comprise a tooth or a peg and may be substantially cylindrical, rectangular, pyramidal, trapezoidal or make take other three dimensional geometrical shapes. The sides of the projection may be sloped. A planar surface may comprise a plurality of projections.
A receptacle in a planar surface adjacent to the planar surface comprising the projection, may comprise a void, a hole, a notch, a track etc. In some embodiments, the receptacle is adapted to receive the projection from the adjacent planar surface.
Torque limiting devices of the present invention are advantageous for use in tools designed to impart a rotational force. A curette is a medical tool used to scrape, score, or otherwise form a cavity or create a void within one of the body's solid organs. A curette comprises a tip that scrapes the bone, or other organ. The tip may be made of any suitable biocompatible material, for example, stainless steel, cobalt chromium, titanium, and alloys or mixtures thereof. Because of the relatively small size of the tip and thin material wall thickness, it is possible that the tip may break or deform when too high a torque is applied to the handle of the curette.
A surgical tool, such as a curette, with a torque limiting device of the present invention, limits the torque applied to the tip of the tool to reduce the possibility of damaging the tool. In addition, the torque limiting device of the present invention may be reengaged so that the tool may be used again immediately after disengagement.
In some embodiments, a surgical tool of the present invention may comprise a rod having a first and a second end, a surgical implement attached to the first end of the rod, and a handle positioned near the second end of the rod. The surgical tool may further comprise a first surface attached to the rod and a second surface attached to the handle, the first surface in frictional contact with the second surface. The first and second surfaces may comprise plates, a notch and a tooth, or any other configuration that will allow disengageable torque translation. When a surgeon applies a torque to the handle, the friction between the first surface and second surface causes the torque to translate to the rod, and consequently, to the surgical implement. If a torque greater than a certain critical torque is applied to the handle, the friction force between the first and second surfaces will be overcome, and the second surface will slip with respect to the first surface, which causes the torque applied to the handle not to be translated to the rod. In addition, after the first and second surfaces slip, they may be reengaged so that the surgeon may immediately continue using the tool.
Accordingly, in some embodiments, the present invention provides a surgical tool that limits torque applied to the surgical implement without permanently deforming or damaging the tool. Therefore, if a surgeon applies too high a torque to the handle of the tool, the tool will disengage without permanently damaging the tool. In addition, the tool may be reengaged so that the surgeon may continue the surgery without delay.
The present invention also provides medical kits. In some embodiments, a medical kit of the present invention comprises a surgical tool of the present invention. The medical kit of the present invention may further comprise additional surgical tools.
A tool, and/or a surgical tool, of the present invention may be used in a manner similar to prior tools and provide the added benefit of being re-settable and thus reusable if a predetermined torque is exceeded. Thus, in some embodiments, a method of the present invention comprises applying a torque to a tool comprising a torque limiting device of the present invention wherein if a predetermined torque is exceeded by an excess torque causing the first and second planar surfaces to rotate independently from each other, the method comprises applying a rotational force to the first planar surface in a direction substantially opposite the direction of the excess torque to re-engage the first and second planar surfaces and cause a rotational force applied to the first planar surface to be transmitted to the second planar surface.
Further details and advantages of the present invention are set forth in the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
For the purposes of this specification, unless otherwise indicated, all numbers expressing quantities, conditions, and so forth used in the specification are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification are approximations that can vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more, e.g. 1 to 6.1, and ending with a maximum value of 10 or less, e.g., 5.5 to 10. Additionally, any reference referred to as being “incorporated herein” is to be understood as being incorporated in its entirety.
It is further noted that, as used in this specification, the singular forms “a,” “an,” and “the” include plural referents unless expressly and unequivocally limited to one referent.
According to certain embodiments, the present invention provides a torque limiting device which may be used with medical devices or other mechanical devices to which a torque is applied. The present invention provides a torque limiting device that may be incorporated into any tool or system that experiences a torque. A device according to the present invention may comprise a rod having a first end and second end. The first and second ends may include the tips of the rod as well as a region of the rod near each tip. The device may further comprise a surgical implement attached to the first end of the rod and a handle positioned near the second end of the rod. The device may further comprise a first surface attached to the rod and a second surface attached to the handle. The two surfaces may be disposed in frictional contact with each other, for example via a tooth and notch. The two surfaces may be contained within a housing, which may be attached to the handle.
The device may further comprise a spring disposed between the housing to force the tooth into the notch when the tooth and notch are aligned. The two surfaces are able to rotate independently, but when the tooth and notch are engaged, the two surfaces rotate together. The tooth and notch may be designed to disengage when a torque equal to or greater than a predetermined maximum torque is applied to the device. The maximum torque is the torque that is required to cause the tooth to rise out of the notch, overcoming the static friction force between the surfaces and the spring force exerted by the spring on the tooth. When the tooth disengages from the notch, the two surfaces rotate independently, and consequently the excessive torque applied to the first surface is not translated to the second surface. The two surfaces may be made of a polymer, stainless steel, aluminum, or any other material or combination of materials suitable for creating friction between the two surfaces.
This torque limiting device may be used, for example, on a curette. A curette may comprise the elements disclosed in PCT Patent Application WO 2005/023085, which is herein incorporated by reference. The disengagement of the tooth from the notch protects the curette tip, for example, from an application of torque that may be sufficient to break the tip while still inserted in the patient.
In addition to limiting the amount of torque that can be applied to the functional implement of the tool, the device of the present invention may be engaged again to resume use. After the tooth disengages from the notch, the device may be reengaged by rotating the first surface until the tooth and notch align, at which point the spring forces the tooth into the notch. When the tooth and notch are engaged again, the use of the tool may resume. The ability to reengage the device is a significant advantage over previous devices, which suffer permanent damage when an excessive torque is applied. Therefore, previous torque limiting devices are useless after one instance of excessive torque, whereas the device of the present invention may be reused after many instances of excessive torque.
The torque limiting device of the present invention may be used on medical tools, such as a curette, as described above. The torque limiting device may also be used on other surgical tools for use in human and veterinary contexts, including tools for grasping, scraping, bending, pushing, or otherwise manipulating an organ of the body, including bone. The device may also be used on other tools or machines in which a maximum torque should not be exceeded. For example, the torque limiting device of the present invention could be included in a screwdriver or wrench to prevent over-tightening of the screw or bolt. The torque limiting device may also be used on machines in which certain components could break when excessive torque is applied.
Referring now to
The torque limiting device 22 may comprise a first plate 24 having a notch 26 and a second plate 28 having a tooth 30. The notch and tooth can be interchangeable, i.e. the first plate can have the tooth and the second plate can have a notch. The tooth 30 and notch 26 may be substantially the same shape and size so that they may fit together. The tooth 30 may be V-shaped, V-shaped with a flat bottom, U-shaped, semi-circular, or any other shape that provides a non-perpendicular angle between the tooth 30 and the surface of the second plate 28. The tooth 30 and the notch 26 may be radially aligned such that the tooth 30 fits into the notch 26 when they are rotationally aligned.
The first plate 24 and the second plate 28 may be disposed within a housing 32. The housing 32 may be generally in the shape of a hollow cylinder having an inner diameter equal to or larger than the diameter of the larger of the first plate 24 and the second plate 28. The housing 32 may comprise a cap 34, and a compression spring 36 may be disposed between the cap 34 and the second plate 28. The second plate 28 may comprise a collar 38 over which the spring 36 fits so that lateral movement of the spring 36 is substantially prevented. The torque limiting device 22 may further comprise at least one guide pin 40, and the second plate 28 may comprise at least one slot 42. The at least one guide pin 40 may be integrally formed with the cap 34 or with the housing 32, or the at least one guide pin 40 may be fixedly attached to the cap 34 or to the housing 32. The second plate 28 may be positioned in the housing 32 such that the at least one guide pin 40 fits into the at least one slot 42. The at least one slot 42 allows the second plate 28 to slide longitudinally along the at least one guide pin 40 but thereby prevents the second plate 28 from rotating with respect to the housing 32. The second plate 28 will then rotate only when the housing 32 rotates.
Conversely, the first plate 24 may be disposed in the housing 32 such that rotational movement of the first plate 24 with respect to the housing 32 is allowed but longitudinal movement with respect to the housing 32 is prevented. This may be accomplished by providing the housing 32 with a support 44, such as a ledge, that contacts the bottom surface of the first plate 24, or by other suitable means. Accordingly, the first plate 24 is permitted to rotate along the support 44 but is not permitted to move longitudinally.
The rod 12 may be integrally formed with the first plate 24 or may be fixedly attached to the first plate 24, such as by welding. Therefore, a rotation of the first plate 24 is directly translated to the rod 12, and consequently to the surgical implement 18.
The housing 32 may be attached to the handle 20. Therefore, a rotation of the handle 20 is directly translated to the housing 32, and consequently, via the at least one guide pin 40, to the second plate 28.
The rotation of the second plate 28 is translated to the first plate 24 by the frictional interface between the tooth 30 and the notch 26. When the tooth 30 and notch 26 are engaged, that is when the tooth 30 and notch 26 are rotationally aligned and the tooth 30 is positioned within the notch 26, rotation of the handle 20 causes rotation of the implement 18.
However, if a torque above a maximum torque is applied to the handle 20, the friction force between the tooth 30 and notch 26 and the spring force of the compression spring 36 may be overcome, and the tooth 30 may disengage from the notch 26, that is the tooth 30 may rise out of the notch 26 and become no longer rotationally aligned. When the tooth 30 is disengaged from the notch 26, a rotation of the handle 20 does not cause a rotation of the implement 18. The tooth 30 and notch 26 may be engaged again by rotating the handle 20 until the tooth 30 and notch 26 are rotationally aligned, and at that point the compression spring 36 will push the tooth 30 into the notch 26 again.
The maximum torque may be determined by varying any of the following: the spring rate of the compression spring; the slope of the tooth and notch; the length and height of the notch; the radial distance of the tooth and notch from the center of the plate and pedestal, respectively; and the materials used for the plate and pedestal. In an embodiment, a surgical tool of the present invention may be designed to slip at about 10±1 in.-lbs. torque and to break at about 13±1 in.-lbs. torque. Thus, if a torque of 13 in.-lb., for example, is required to break the coupling between the rod 12 and the surgical implement 18, the tooth and notch may be designed to slip and begin to disengage when a torque of approximately 10 in.-lb, for example, is applied to the handle 20, and then completely disengage when 13 in.-lb. is applied to handle 20 As a result, a torque of 15 in.-lb. would never be transmitted to the rod 12 because the tooth 30 would disengage from the notch 26 at a torque of 13 in.-lb. Furthermore, it has been found that the mean torque required to scrape normal bone is approximately 2.0 in.-lb. Therefore, a configuration that caused disengagement to begin at 10 in.-lb and complete at 13 in.-lb. would allow a torque that is required for normal scraping to be translated to the surgical implement.
Referring now to
The torque limiting device 122 may comprise a plate 124 having a depression 126 and a ball plunger 128 having a ball 130. The ball 130 and depression 126 may be substantially the same shape and size so that they may fit together. The ball 30 may be V-shaped, V-shaped with a flat bottom, U-shaped, semi-circular, or any other suitable shape. The ball 130 and the depression 126 may be radially aligned such that the ball 130 fits into the depression 126 when they are rotationally aligned. The ball plunger 128 may comprise other components, as is commonly known. For example, the ball plunger 128 may comprise a hollow cylinder, partially within which the ball slides longitudinally. The ball plunger 128 may also comprise a shaft that limits the movement of the ball and a spring that tends to push the ball longitudinally in the cylinder. The ball plunger 128 may also have other configurations that allow for longitudinal movement of the ball.
The plate 124 and the ball plunger 128 may be disposed within a housing 132. The housing 132 may be generally in the shape of a hollow cylinder having an inner diameter equal to or larger than the diameter of the plate 124. The housing 132 may comprise a cap 134, and the ball plunger 128 may be mounted or attached to the cap 134. Therefore, a rotation of the housing 132 also results in a rotation of the ball plunger 128.
The plate 124 may be disposed within the housing 132 such that rotational movement of the plate 124 is allowed but longitudinal movement with respect to the housing 132 is prevented. This may be accomplished by providing the housing 132 with a support 144, such as a ledge, that contacts the bottom surface of the plate 124, or by other suitable means.
The rod 112 may be integrally formed with the plate 124 or may be fixedly attached to the plate 124, such as by welding. Therefore, a rotation of the plate 124 is directly translated to the rod 112, and consequently to the surgical implement 118.
The housing 132 may further comprise a flange 136 attached to the cap 134. The handle 120 may be attached to the housing 132 by fitting over the flange 136 in a relatively tight tolerance. Accordingly, a rotational movement of the handle 120 would be translated through the flange 136 to the housing 132, and therefore to the ball plunger 128.
The rotation of the ball plunger 128 is translated to the plate 124 by the frictional interface between the ball 130 and the depression 126. When the ball 130 and depression 126 are engaged, that is when the ball 130 and depression 126 are rotationally aligned and the ball 130 is positioned within the depression 126, rotation of the handle 120 causes rotation of the implement 118.
However, when the torque applied to the handle 120 exceeds a certain predetermined amount, the ball plunger 128 may compress and the ball 130 of the ball plunger 128 may rise out of the depression 126 to a disengaged position. When the ball 130 and depression 126 are disengaged, a rotation of the handle 120 no longer causes a rotation of the implement 118. The ball 130 and depression 126 may be engaged again by rotating the handle 120 until the ball 130 and depression 126 are rotationally aligned, and at that point the ball plunger 128 will expand so that the ball 130 again rests in the depression 126.
The maximum torque may be determined by varying any of the following, as described above: the spring rate of the compression spring in the ball plunger; the shape and size of the ball and depression; the radial distance of the ball and depression from the center of the plate; and the materials used for the ball and the plate.
The present invention may also comprise a method for using the device as described above. Referring now to
While the invention has been described with reference to certain embodiments, other features may be included without departing from the spirit and scope of the invention.
Claims
1. A surgical device comprising:
- a rod having a first end and a second end;
- a surgical implement attached to the first end of the rod;
- a handle positioned near the second end of the rod;
- a first surface attached to the rod; and
- a second surface attached to the handle, the second surface in frictional contact with the first surface such that a rotation of the handle causes a rotation of the rod,
- wherein when the rotation of the handle exceeds a maximum torque, the second surface disengages from the first surface, so that the rotation of the handle does not cause rotation of the rod.
2. The surgical device of claim 1 further comprising a housing attached to the handle.
3. The surgical device of claim 2, wherein the housing defines a cavity within which the first and second surfaces are positioned.
4. The surgical device of claim 2, wherein the first surface comprises a first plate having a notch and the second surface comprises a second plate having a tooth.
5. The surgical device of claim 4, wherein the notch and the tooth are substantially the same size and shape.
6. The surgical device of claim 4 further comprising a compression spring disposed between the housing and the second surface, the spring exerting a force on the second surface to engage the tooth with the notch.
7. The surgical device of claim 4, the housing further comprising a support that substantially prevents movement of the first surface in one direction along an axis of the rod.
8. The surgical device of claim 2, wherein the first surface comprises a disk having a depression and the second surface comprises a ball of a ball plunger.
9. The surgical device of claim 8, wherein the depression and the ball are substantially the same size and shape.
10. A surgical device comprising:
- a rod comprising a first section and a second section, the first section rotatably connected to the second section;
- an implement attached to the first section of the rod;
- a handle attached to the second section of the rod;
- a first plate attached to the first section of the rod, the first plate having a depression;
- a second plate attached to the second section of the rod, the second plate raised portion of substantially the same size and shape as the depression of the first plate;
- a housing that defines a cavity, the first plate and second plate fitting inside the cavity and the first plate restrained within the housing by a ledge; and
- a compression spring disposed between a cap of the housing and a surface of the second plate such that the spring pushes the second plate longitudinally away from the cap of the housing,
- wherein the raised portion of the second plate engages with the depression of the first plate when the raised portion and the depression are aligned, so that a rotation of the second section of the rod causes a rotation of the first section of the rod, and
- wherein when the rotation of the second section of the rod exceeds a maximum torque, the spring compresses and the raised portion of the second plate disengages from the depression of the first plate, so that the rotation of the second section does not cause rotation of the first section.
11. The surgical device of claim 10, the rod comprising a cylindrical tube.
12. The surgical device of claim 11 further comprising an actuator disposed within the rod and operable to activate the implement.
13. The surgical device of claim 12 further comprising a trigger positioned on the handle operable to control the actuator.
14. A surgical device comprising:
- a rod;
- a surgical implement attached to a first end of the rod;
- a handle positioned near a second end of the rod;
- a ball plunger attached to the handle, the ball plunger comprising a ball housed in a cylinder and pushed longitudinally by a spring contained within the cylinder; and
- a disk attached to the rod, the disk having a depression of substantially the same size and shape as the ball of the ball plunger,
- wherein the ball of the ball plunger may fit into the depression of the disk so that a rotation of the handle causes rotation of the rod, and
- wherein when the rotation of the handle exceeds a maximum torque, the spring of the ball plunger compresses and the ball of the ball plunger rises out of the depression of the disk, so that the rotation of the handle does not cause rotation of the rod.
15. The surgical device of claim 14 further comprising a housing attached to the handle and the ball plunger, the housing defining a cavity in which the disk and ball plunger are positioned.
16. The surgical device of claim 15, the cavity having a substantially cylindrical shape and a diameter.
17. The surgical device of claim 16, wherein the disk has a diameter and the diameter of the cavity is between 0 and 10 millimeters larger than the diameter of the disk.
18. The surgical device of claim 14, the handle having a cavity for receiving the second end of the rod.
19. The surgical device of claim 15, the housing comprising a means for limiting a longitudinal movement of the rod.
20. A method for using a surgical tool having a torque limiting device comprising the steps of:
- inserting a surgical tool having a rod, a surgical implement, and a handle into a body;
- positioning the surgical implement at a desired location within the body;
- applying a torque to the handle;
- reengaging the tool after an excessive torque is applied to the handle.
21. The method of claim 20, wherein the surgical tool further comprises a first surface and a second surface in frictional contact with the second surface, and wherein the step of reengaging the tool comprises realigning the first surface with the second surface.
Type: Application
Filed: Oct 21, 2005
Publication Date: Jan 11, 2007
Inventor: Christopher Phan (San Leandro, CA)
Application Number: 11/256,036
International Classification: B25B 23/157 (20060101);
