Joint mechanism and prosthetic hand using the same

Abstract

The present invention provides a joint mechanism and a prosthetic hand using it, in which the force required to move the support in one direction is relatively weak, and the force required to move the support in the other direction is relatively strong. [Solution] The joint mechanism has an elastically deformable elastic part surrounding the shaft and a support part connected to the elastic part. When the support part is displaced in one direction along the circumferential direction of the shaft, a first frictional force acts between the elastic part and the outer surface of the shaft. When the support part is displaced in the other direction along the circumferential direction of the shaft, a second frictional force acts between the elastic part and the outer surface of the shaft, and the first frictional force is greater than the second frictional force.

Description

Technical Field

[0001] The present invention relates to a joint mechanism and a prosthetic hand using the same.

Background Art

[0002] For those with congenital or acquired defects or malformations in the palm due to congenital causes or accidents, etc., a prosthetic hand equipped with a hand tool for restoring the shape and function of the hand is worn.

[0003] For example, Patent Document 1 discloses a finger drive unit of an electric prosthetic hand provided with a piston that moves forward and backward by a feed screw that rotates via a reduction gear with the rotation of a motor, a middle joint member that is connected to a proximal joint member that rotates in response to the movement of the piston, and a distal joint member that is connected to the middle joint member. When the proximal joint member rotates, the first sliding contact portion of the proximal joint member can bend a first wire member installed between the middle joint member and the main body into a U shape.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The prosthetic hand of Patent Document 1 has a relatively large structure and can be used, for example, as a prosthetic hand for adults. In contrast, the fingers of infants are thinner and shorter than those of adults, and their shapes are also diverse. Therefore, prosthetic hands for infants are likely to be made-to-order products. Moreover, due to space limitations, it is difficult to use a prosthetic hand for adults such as that in Patent Document 1. Furthermore, there is also the actual situation that the cost involved in manufacturing the prosthetic hand is restricted in order to suppress the burden on caregivers and the like.

[0006] On the other hand, even if the prosthetic finger cannot be actively moved, a prosthetic hand with a joint mechanism that can fix the prosthetic finger in the moved position allows the user to lift an object by fixing the prosthetic finger in a grasping position. Furthermore, such a joint mechanism has a relatively simple structure and can be manufactured inexpensively, making it particularly effective for prosthetic hands for infants and young children. One example of such a joint mechanism is a friction joint mechanism that generates a strong frictional force at the pivot point of the joint connected to the prosthetic finger, thereby fixing the prosthetic finger in place.

[0007] However, because the strength of an infant's fingers is weaker than that of an adult, if sufficient frictional force is applied to the friction joint mechanism to grasp an object, there is a problem in that the infant cannot push the prosthetic finger in to grasp the object. On the other hand, if the friction joint mechanism is designed to reduce the frictional force to the point where an infant can push the prosthetic finger in to grasp an object, the gripping force will be insufficient, creating a dilemma.

[0008] Therefore, a small friction joint mechanism that possesses enough frictional force to grip and swing an object without it falling, and that can be used in prosthetic hands for infants and toddlers, has yet to be realized.

[0009] This invention has been made in view of the problems of the prior art, and aims to provide a joint mechanism and a prosthetic hand using the same, in which the force required to move the support in one direction is relatively weak, and the force required to move the support in the other direction is relatively strong. [Means for solving the problem]

[0010] To achieve the above objective, one representative joint mechanism of the present invention is: An elastically deformable elastic part surrounding the shaft, It has a support portion connected to the elastic portion, When the support portion is displaced in one direction along the circumferential direction of the shaft portion, a first frictional force acts between the elastic portion and the outer circumferential surface of the shaft portion. When the support portion is displaced in another direction along the circumferential direction of the shaft portion, a second frictional force acts between the elastic portion and the outer circumferential surface of the shaft portion. This is achieved by the first frictional force being greater than the second frictional force. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a joint mechanism and a prosthetic hand using the same, in which the force required to move the support in one direction is relatively weak, and the force required to move the support in the other direction is relatively strong. Other issues, configurations, and effects not mentioned above will be clarified by the following description of the embodiments. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a perspective view of a prosthetic hand equipped with a joint mechanism according to an embodiment of the present invention. [Figure 2] Figure 2 is a perspective view showing a prosthetic finger modeled after the index finger used in a prosthetic hand. [Figure 3] Figure 3 is a perspective view of the friction joint. [Figure 4] Figure 4 shows the friction joint section in an unfolded state. [Modes for carrying out the invention]

[0013] "Rotational friction" refers to the friction that occurs between a shaft and a rotating body that engages with the shaft. In this case, the frictional force between the shaft and the rotating body is proportional to the coefficient of friction and the contact force between the shaft and the rotating body. The contact force between the shaft and the rotating body is equivalent to the force with which the rotating body grips the shaft, and therefore it is proportional to the difference between the diameter of the rotating body and the diameter of the shaft.

[0014] The joint mechanism of this embodiment is similar to a so-called clamp spring and has a cylindrical portion that can engage with a shaft, and support portions and protrusions that extend radially from both circumferential ends of the cylindrical portion. The inventor focused on the phenomenon that the inner diameter of the cylindrical portion in a free state increases or decreases by relatively displacing these support portions and protrusions. By utilizing this phenomenon, when engaged with the shaft, the frictional force between the shaft and the cylindrical portion can be increased by relatively displacing the support portions and protrusions in a direction that decreases the inner diameter of the cylindrical portion, and the frictional force between the shaft and the cylindrical portion can be decreased by relatively displacing the support portions and protrusions in a direction that increases the inner diameter of the cylindrical portion, thereby creating a one-way clutch-like action.

[0015] In this embodiment, the above phenomenon is applied to provide a joint mechanism that generates rotational friction at the base of the prosthetic finger by fixing the prosthetic finger to a support part. At this time, a rotational moment is generated in the support part to which the prosthetic finger is fixed, but until just before the rotational movement of the cylindrical part and the shaft part occurs, the relationship of force equilibrium causes the cylindrical part to deform in a way that reduces its diameter. As a result, when the prosthetic finger is closed, the rotational friction is increased by connecting the joint mechanism in such a way that the outer circumference of the cylindrical part decreases, so that, for example, an object can be grasped. Furthermore, by connecting the prosthetic finger and the joint mechanism in this way, when the prosthetic finger is opened, the outer circumference of the cylindrical part increases, so rotational friction is reduced, and the action of releasing an object can be easily performed. The prosthetic hand including the joint mechanism of the present invention will be described below with reference to the drawings.

[0016] Figure 1 is a perspective view of a prosthetic hand 1 equipped with a joint mechanism according to an embodiment of the present invention. Figure 2 is a perspective view showing a prosthetic finger modeled after an index finger used in the prosthetic hand 1. Figure 3 is a perspective view of the friction joint portion 41. Figure 4 is a diagram showing the friction joint portion 41 in an unfolded state.

[0017] In FIG. 1, the prosthetic hand 1 has a base tube 2 bent in an L shape and five prosthetic fingers (joint mechanisms) 3 to 7 attached to the base tube 2. The base tube 2 has a cylindrical short-axis portion 2a and a cylindrical long-axis portion 2b that intersects the short-axis portion 2a at a substantially right angle. It is preferable that the axis of the short-axis portion 2a and the axis of the long-axis portion 2b are in a non-parallel relationship. Thereby, the moving directions of the prosthetic finger 3 and the prosthetic fingers 4 to 7 can be made different, and for example, operations such as picking up an object can be performed by the prosthetic finger 3 and the prosthetic fingers 4 to 7.

[0018] The prosthetic finger 3 corresponding to the thumb is attached to the short-axis portion 2a, and the prosthetic finger 4 corresponding to the index finger, the prosthetic finger 5 corresponding to the middle finger, the prosthetic finger 6 corresponding to the ring finger, and the prosthetic finger 7 corresponding to the little finger are attached to the long-axis portion 2b.

[0019] The prosthetic finger 3 has a friction joint portion 31, a first joint portion 32, a second joint portion 33, and a third joint portion 34.

[0020] The prosthetic finger 4 has a friction joint portion 41, a first joint portion 42, a second joint portion 43, and a third joint portion 44.

[0021] The prosthetic finger 5 has a friction joint portion 51, a first joint portion 52, a second joint portion 53, and a third joint portion 54.

[0022] The prosthetic finger 6 has a friction joint portion 61, a first joint portion 62, a second joint portion 63, and a third joint portion 64.

[0023] The prosthetic finger 7 has a friction joint portion 71, a first joint portion 72, a second joint portion 73, and a third joint portion 74.

[0024] Here, referring to FIGS. 2 to 4, the prosthetic finger 4 will be described. However, since the prosthetic fingers 3 and 5 to 7 have the same configuration including the friction joint portion, duplicate descriptions will be omitted.

[0025] In FIG. 3, the friction joint portion 41 is composed of a cylindrical portion (elastic portion) 41a, a protruding portion 41b connected to one circumferential end of the cylindrical portion 41a, and a connecting portion 41c connected to the other circumferential end of the cylindrical portion 41a.

[0026] The friction joint portion 41 can be formed from an elastically deformable flat plate material FP as shown in Figure 4. The flat plate material FP consists of, for example, a spring plate punched out in a strip shape by press molding, with a rectangular projection E1 formed at the center of one end in the longitudinal direction, and a rectangular frame portion E2 with a rectangular opening formed at the other end. The width of the projection E1 perpendicular to the longitudinal direction is approximately equal to the opening width of the rectangular frame portion E2.

[0027] Along the dotted lines A and B in Figure 4, the material FP is bent at right angles near both ends, and the material between dotted lines A and B is wound into a cylindrical shape so that the bent portions protrude outwards, thereby forming the friction joint portion 41. At this time, as shown in Figure 3, when the protruding portion E1 is wound into a cylindrical shape after passing through the rectangular frame portion E2, a part of the protruding portion E1 (curved portion E1a) is aligned axially with a part of the rectangular frame portion E2 (curved portion E2a), and these constitute a part of the cylindrical portion 41a surrounding the shaft portion. In addition, the remaining portion of the protruding portion E1 (flat portion E1b) forms a flat protruding portion 41b, and the remaining portion of the rectangular frame portion E2 (flat portion E2b) forms a gate-shaped connecting portion 41c as a support portion, and these extend in the radial direction of the cylindrical portion 41a. The curved portion E1a does not necessarily need to be aligned axially with respect to the curved portion E2a, but it is preferable that the cylindrical portion 41a surrounds the long axis portion 2b beyond half its circumference in order to attach the prosthetic finger 4 to the outer circumference of the long axis portion 2b.

[0028] In the free state shown in Figure 3, the inner diameter of the cylindrical portion 41a is φ1. On the other hand, the outer diameter of the long axis portion 2b shown in Figure 2 is φ2, and φ2 > φ1.

[0029] The first joint portion 42 has a shape in which the center of an elongated flat plate is twisted at approximately a right angle, and one end is connected to the connecting portion 41c by, for example, welding or screwing. The third joint portion 44 also has a shape in which the center of a flat plate is twisted at approximately a right angle.

[0030] The second joint portion 43 has an elongated, casing-like shape and has slits 43a and 43b at both ends. The other end of the first joint portion 42 is housed in slit 43a and is connected to it so as to be rotatable relative to it using a screw (not shown). One end of the third joint portion 44 is housed in slit 43b and is connected to it so as to be rotatable relative to it using a screw (not shown). As a result, the pivot angle between the first joint portion 42 and the second joint portion 43 is adjustable, and the pivot angle between the third joint portion 44 and the second joint portion 43 is also adjustable. After adjustment, the first joint portion 42, the second joint portion 43, and the third joint portion 44 are connected to the friction joint portion 41 with their relative displacements fixed by tightening the screws.

[0031] When attaching the prosthetic finger 4 to the outer circumference of the long shaft portion 2b, a force is applied in a direction that brings the protruding portion 41b and the connecting portion 41c closer together. This expands the inner diameter of the cylindrical portion 41a, making it larger than the outer diameter of the long shaft portion 2b, so that the cylindrical portion 41a can be inserted integrally with the prosthetic finger 4 from the end of the long shaft portion 2b. By removing the force that brings the protruding portion 41b and the connecting portion 41c closer together, the cylindrical portion 41a shrinks in diameter due to its own elastic force, so its inner circumferential surface comes into close contact with the outer circumferential surface of the long shaft portion 2b, generating a relatively strong frictional force (intermediate frictional force) between the two surfaces, which fixes the prosthetic finger 4 to the long shaft portion 2b.

[0032] In a similar manner, the prosthetic fingers 5 to 7 can be attached to the long shaft portion 2b in this order, and the prosthetic finger 3 can be attached to the short shaft portion 2a.

[0033] The following describes the action of a wearer, with prosthetic hand 1 attached to one hand, grasping (holding) an object with prosthetic fingers 4 and 3. As shown in Figure 1, prosthetic fingers 4 and 3 are positioned opposite each other, and the object to be grasped (not shown) is assumed to be between prosthetic fingers 4 and 3. Here, in order to grasp the object, it is necessary to push prosthetic finger 4 towards the object, and when releasing the grasped object, it is necessary to pull prosthetic finger 4 away from the object. Generally, the force with which a person pushes is relatively small, while the force with which a person pulls is considered to be larger.

[0034] First, when the wearer attempts to rotate the prosthetic finger 4 in direction C (the other direction along the circumferential direction of the long axis portion 2b) with their other hand, the force in direction C is transmitted to the connecting portion 41c. At this time, due to the lever principle, the wearer's force is amplified and transmitted to the connecting portion 41c, so that the connecting portion 41c can be brought closer to the protruding portion 41b with relatively little force. As a result, the inner diameter of the cylindrical portion 41a expands, and its inner circumferential surface is displaced so that it separates from the outer circumferential surface of the long axis portion 2b.

[0035] As a result, the frictional force generated between the inner surface of the cylindrical portion 41a and the outer surface of the long shaft portion 2b decreases, changing from an intermediate frictional force to a low frictional force (second frictional force). This allows the wearer to easily pivot the prosthetic finger 4 relative to the long shaft portion 2b against the low frictional force, enabling the prosthetic finger 4 to be pushed against an object.

[0036] After grasping an object with the prosthetic fingers 4 and 3, when the wearer releases the force pushing on the prosthetic finger 4, the cylindrical portion 41a returns to its original elastic state, and the frictional force generated between the inner surface of the cylindrical portion 41a and the outer surface of the long axis portion 2b returns to an intermediate frictional force. Furthermore, when a counterforce is generated from the object, a moment in direction D in Figure 3 is transmitted to the prosthetic finger 4, and at this time, a force in direction D (one direction along the circumferential direction of the long axis portion 2b) is transmitted to the connecting portion 41c in Figure 3. As a result, the inner surface of the cylindrical portion 41a is pressed against the outer surface of the long axis portion 2b, the inner diameter of the cylindrical portion 41a shrinks so that the gap between the two surfaces decreases, and a high frictional force (first frictional force) higher than the low frictional force is applied between the two surfaces. This fixes the prosthetic finger 4 to the long axis portion 2b, and even if the object is swung around, the gripping state between the prosthetic fingers 4 and 3 can be maintained.

[0037] On the other hand, when the wearer pulls the prosthetic finger 4 away from the object with their other hand (direction D in Figure 3), they can exert a stronger force than the pushing force. This pulling force can be used to rotate the prosthetic finger 4 relative to the long axis portion 2b, thereby allowing them to release their hand from the object.

[0038] According to this embodiment, even wearers with relatively weak strength, such as infants, can easily push in the prosthetic finger with one hand. Furthermore, once an object is grasped by the prosthetic finger, the gripping force is relatively strong, allowing it to perform a sufficient gripping function as a prosthetic hand. In addition, because the joint mechanism of this embodiment is a simple mechanism that utilizes friction, the manufacturing cost of the prosthetic hand is low, and it is easy to replace prosthetic fingers of different lengths as the wearer grows.

[0039] Furthermore, the embodiments are not limited to those described above. For example, an interference part made of a heat-shrinkable material (e.g., a rubber membrane) can be placed between the outer circumferential surface of the shaft and the inner circumferential surface of the cylindrical part to increase the frictional force between the two surfaces. Also, the joint mechanism does not necessarily have to have a protruding part. The joint mechanism of the present invention can be used not only for prosthetic hands but also for other applications.

[0040] This specification includes disclosures of the following inventions. (First aspect) An elastically deformable elastic part surrounding the shaft, It has a support portion connected to the elastic portion, When the support portion is displaced in one direction along the circumferential direction of the shaft portion, a first frictional force acts between the elastic portion and the outer circumferential surface of the shaft portion. When the support portion is displaced in another direction along the circumferential direction of the shaft portion, a second frictional force acts between the elastic portion and the outer circumferential surface of the shaft portion. The first frictional force is greater than the second frictional force. A joint mechanism characterized by the following features.

[0041] (Second aspect) The elastic part is a leaf spring wound around the shaft portion beyond half its circumference, and the support portion is connected in such a way that the elastic part expands in diameter in accordance with the displacement of the support portion in one direction and elastically contracts in diameter in accordance with the displacement of the support portion in the other direction.

[0042] (Third aspect) One end of the leaf spring protrudes radially from the shaft and is connected to the support portion. A second embodiment of the joint mechanism characterized by the following:

[0043] (Fourth aspect) An articulated mechanism according to any of the first to third embodiments, further comprising an interference portion disposed between the shaft portion and the elastic portion and made of a heat-shrinkable material.

[0044] (Fifth aspect) Having a joint mechanism according to any of the first to third embodiments, the support portion is connected to the prosthetic finger. A prosthetic arm characterized by the following features.

[0045] (Sixth aspect) Two of the aforementioned joint mechanisms are provided. The axis of the shaft to which one of the joint mechanisms is attached and the axis of the shaft to which the other joint mechanism is attached are not parallel. A fifth embodiment of a prosthetic arm characterized by the following: [Explanation of Symbols]

[0046] 1. Prosthetic arm 2 Base tubes 3-7 Prosthetic fingers 41-71 Friction joint area 42-72 First joint 43-73 Section 2 of the Sekibu Chapter 44-74 Third joint 41a Cylindrical part 41b Projection 41c Connection part

Claims

1. An elastically deformable elastic part surrounding the shaft, It has a support portion connected to the elastic portion, When the support portion is displaced in one direction along the circumferential direction of the shaft portion, a first frictional force acts between the elastic portion and the outer circumferential surface of the shaft portion. When the support portion is displaced in another direction along the circumferential direction of the shaft portion, a second frictional force acts between the elastic portion and the outer circumferential surface of the shaft portion. The first frictional force is greater than the second frictional force. A joint mechanism characterized by the following features.

2. The joint mechanism according to claim 1, wherein the elastic part is a leaf spring wound around the shaft portion beyond half its circumference, and the support portion is connected such that the elastic part expands in diameter in accordance with the displacement of the support portion in one direction and elastically contracts in diameter in accordance with the displacement of the support portion in the other direction.

3. One end of the leaf spring protrudes radially from the shaft and is connected to the support portion. The joint mechanism according to feature 2.

4. The joint mechanism according to claim 1, further comprising an interference portion disposed between the shaft portion and the elastic portion and made of a heat-shrinkable material.

5. The joint mechanism is as described in any one of claims 1 to 4, and the support portion is connected to the prosthetic finger. A prosthetic arm characterized by the following features.

6. Two of the aforementioned joint mechanisms are provided, The axis of the shaft to which one of the joint mechanisms is attached and the axis of the shaft to which the other joint mechanism is attached are not parallel. The prosthetic hand according to feature 5.

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