Parallel linkage and artificial joint device using the same

There are provided an artificial joint device that can realize an artificial limb enabling twisting motion without a drive source, and when with the drive source, reduce the size and costs of the device, and a parallel linkage that can realize the device. The linkage connects a foot portion and a mounting plate spaced from each other. A fixed link has one end fixed to the plate, and the other end connected to the foot portion via a ball joint, making the angle of the fixed link relative to the foot portion changeable in any direction. Expansible links extend between the foot portion and the plate in an expansible/contractible manner and each have opposite ends connected to the plate and the foot portion via respective upper and lower ball joints, making respective angles thereof relative to the foot portion and the plate changeable in any direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an artificial joint device and a parallel linkage, which are applied to an artificial limb, such as a prosthetic limb or a limb of a robot.

2. Description of the Prior Art

Conventionally, an artificial joint device of the above-mentioned kind has been disclosed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 11-345. The artificial joint device is applied to an ankle joint for connecting between a foot portion of an artificial leg and a leg portion of the same. The foot portion of the artificial leg has an upper end portion thereof formed with a through hole extending laterally. On the other hand, the leg portion of the artificial leg has a lower end thereof bifurcated into two arms to form a bracket with each arm having a hole formed therethrough at a location corresponding to an opening of the through hole extending laterally through the foot portion. In this artificial joint device, a shaft is fitted through the holes of the bracket and the through hole of the foot portion, which are aligned with each other, whereby the foot portion and the leg portion are capable of performing pivotal motion with respect to each other about a horizontal axis, only in the front-rear direction.

According to the above conventional artificial joint device, since the foot portion and the leg portion are allowed to perform pivotal motion with respect to each other about the horizontal axis, only in the front-rear direction, even when a person wearing the artificial leg tries to turn left or right while walking, the ankle joint portion cannot be twisted, which makes the turning motion difficult to perform. A combination of a serial linkage having three or more degrees of freedom and electric motors, used as a joint portion of a limb of a robot, is known as an artificial joint device capable of performing the twisting motion. However, this kind of artificial joint device needs at least three electric motors so as to ensure the three or more degrees of freedom and at the same time support the weight of the components of the robot. This increases the size of a power supply and that of the whole device, resulting in increased manufacturing costs of the device. Further, the increased device size and the necessity of the power supply make it difficult to apply the device to a prosthetic limb.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an artificial joint device which makes it possible to realize a prosthetic limb or the like capable of performing twisting motion without a drive source, and if the drive source is provided, achieve reduction of both the size and manufacturing costs of the artificial joint device itself, and a parallel linkage which makes it possible to realize the artificial joint device.

To attain the above object, according to a first aspect of the invention, there is provided a parallel linkage for connecting two link mounting portions spaced from each other, comprising:

a fixed link having one end thereof fixed to one of the link mounting portions;

a fixed-link joint for connecting another end of the fixed link to another of the link mounting portions such that an angle of the fixed link with respect to the another of the link mounting portions can be changed in any desired direction;

a plurality of expansible links extending between the two link mounting portions in an expansible/contractible manner; and

a plurality of expansible-link joints respectively connecting opposite ends of the plurality of expansible links to the link mounting portions such that respective angles of each expansible link with respect to the link mounting portions can be changed in any desired direction.

According to this parallel linkage, one end of the fixed link is fixed to one of the link mounting portions. Therefore, by making the fixed link solid and robust, it is possible to bear most of compressive load or tensile load applied to at least one of the link mounting portions by the fixed link. In addition, since each of the plurality of expansible links has the opposite ends thereof connected to the two link mounting portions via expansible-link joints associated therewith, respectively, such that the angles thereof with respect to the respective link mounting portions can be changed in any desired direction, no bending stress is applied to the expansible links, but only compressive load and/or tensile load are applied to the same. This makes it possible to use expansible links having relatively low strength and rigidity, thereby reducing the weight of the parallel linkage. Further, the other end of the fixed link and the opposite ends of the expansible links are each connected to the corresponding link mounting portion via the fixed-link joint or the expansible-link joint such that the angle thereof with respect to the link mounting portion can be changed in any desired direction, which ensures a high degree of freedom in the angle of relative motion between the two link mounting portions to thereby enable e.g. twisting motion therebetween.

Preferably, the parallel linkage further comprises urging members provided in the plurality of expansible links, respectively, each for urging a corresponding one of the expansible links in at least one opposite direction to directions in which the expansible link expands and contracts, when the expansible link expands and contracts.

According to this preferred embodiment, since each expansible link is urged by the corresponding urging member in a direction or directions opposite to the expanding direction and/or the contracting direction, it is possible to reduce shock transmitted between the two link mounting portions via the expansible links, by the urging forces. Further, as the amount of contraction or expansion of the expansible link is larger, the urging force of the corresponding urging member is increased, so that the movable range of the expansible link can be properly limited so as to prevent the link mounting portions from moving more than necessary. As a result, even when the link mounting portions are moved e.g. along a curved surface or a three-dimensional object, it is possible to prevent occurrence of wobbling, thereby maintaining excellent follow-up performance.

Preferably, the fixed link includes a shock-absorbing member for absorbing shock transmitted between the two link mounting portions.

According to this preferred embodiment, it is possible to absorb shock transmitted between the two link mounting portions via the fixed link, by the shock-absorbing member.

Preferably, the plurality of expansible links are at least three expansible links.

According to this preferred embodiment, since the two link mounting portions are connected to each other via at least three expansible links and the fixed link, when the expansible links are each actuated e.g. by an actuator for expansion and contraction, it is possible to actuate the expansible links in a manner such that the expansible links twist the two link mounting portions in respective opposite rotating directions.

More preferably, the at least three expansible links are arranged such that connecting portions thereof connected to at least one of the two link mounting portions are not in a line on the at least one of the two link mounting portions, and that a connecting portion of the fixed link is positioned within a polygon defined by the connecting portions of the at least three expansible links as vertexes.

According to this preferred embodiment, since the at least three expansible links are arranged such that connecting portions thereof connected to at least one of the two link mounting portions are not in a line on the link mounting portion, and that a connecting portion of the fixed link is positioned within a polygon defined by the connecting portions of the at least three expansible links as vertexes, it is possible to make compact in size the parallel linkage capable of twisting the two link mounting portions in the respective opposite rotating directions as described above. Further, a driving force required for causing the twisting operation can be reduced, which contributes to enhancement of operating efficiency.

More preferably, the parallel linkage further comprises a drive source, actuators each for actuating a corresponding one of the at least three expansible links for expansion and contraction by a driving force supplied from the drive source, and control means for controlling the driving force supplied to the each actuator from the drive source.

According to this preferred embodiment, since the control means can control expansion and contraction of each of the at least three expansible links via the actuator, it is possible to actuate the expansible links to twist the two link mounting portions in the respective opposite rotating directions as described above, and hence the parallel linkage can be applied to a robot and an industrial machine necessitating such twisting motions. Further, as described hereinbefore, when the fixed link is made solid and robust, the fixed link can bear most of compressive load and tensile load applied to at least one of the link mounting portions, which enables reduction of the driving forces supplied to the actuators for actuating the expansible links, thereby contributing to reduction of energy consumption.

Further preferably, the actuator is an electric actuator configured to produce regenerative power when the corresponding expansible link is expanded and contracted by an external force, and the parallel linkage further comprises an accumulator for storing the regenerative power produced by the electric actuator.

According to this preferred embodiment, since the electric actuators are capable of producing regenerative power when the expansible links are expanded and contracted by external forces, it is possible to utilize the regenerative power as electric power for driving the electric actuators. This makes it possible to reduce both the size of a power supply and the running costs, which contributes to reduction of manufacturing costs of the parallel linkage.

To attain the above object, according to a second aspect of the invention, there is provided an artificial joint device comprising:

two limb members spaced from each other; and

a parallel linkage connecting the two limb members.

According to this artificial joint device, since the two limb members are connected by the parallel linkage, it is possible to enhance the degree of freedom in the angle of relative motion between the two limb members to a level similar to that of a joint of a living body, which has been unattainable by the artificial joint device of the conventional artificial leg. Further, differently from an artificial joint device of a serial linkage type conventionally used e.g. in a robot, the artificial joint device according to this aspect of the invention can be realized without using any power supply or electric motor, but by using the parallel linkage which is simpler and less expensive than the serial linkage.

Preferably, the parallel linkage comprises a fixed link having one end thereof fixed to one of the limb members, a fixed-link joint for connecting another end of the fixed link to another of the limb members such that an angle of the fixed link with respect to the another of the limb members can be changed in any desired direction, a plurality of expansible links extending between the two limb members in an expansible/contractible manner, and a plurality of expansible-link joints respectively connecting opposite ends of the plurality of expansible links to the limb members such that respective angles of each expansible link with respect to the limb members can be changed in any desired direction.

According to this preferred embodiment, the same advantageous effects as provided by the above parallel linkage can be obtained. More specifically, it is possible to reduce the weight of the artificial joint device and achieve a high degree of freedom of the same. Therefore, when the artificial joint device is applied e.g. to an ankle joint of an artificial leg, it is possible to reduce the weight of the artificial leg, and at the same time, differently from the artificial joint of the conventional artificial leg, the artificial joint of the preferred embodiment enables a user to perform e.g. twisting motion or the like between a leg portion and a foot portion, similarly to an ankle joint of a living leg, while support his weight by the artificial leg. This enables the user to perform smoother and more natural motion not only in walking straight ahead but also in turning left or right while walking. Similarly, when the artificial joint device is applied e.g. to a wrist joint of an artificial arm, the weight of the artificial arm can be reduced, and at the same time, the artificial joint enables twisting motion or the like to be performed between an arm portion and a hand portion. In short, the artificial joint makes it possible to enhance the degree of freedom in the angle of motion between the arm portion and the hand portion.

More preferably, the artificial joint device further comprises urging members provided in the plurality of expansible links, respectively, each for urging a corresponding one of the expansible links in at least one opposite direction to directions in which the expansible link expands and contracts, when the expansible link expands and contracts.

According to this preferred embodiment, the same advantageous effects as provided by the above parallel linkage can be obtained. More specifically, it is possible to absorb shock transmitted between the two limb members via the expansible links. Therefore, when the artificial joint device is applied e.g. to an ankle joint of an artificial leg, the urging members serve to soften shock transmitted from the artificial leg to a user's living body via the expansible links when the user puts the artificial leg on a floor, a road surface, or the like (hereinafter simply referred to as “the floor”), to thereby reduce burden on the user wearing the artificial leg. In addition, if the urging members urge the respective expansible links when they contract, in a direction opposite to the contracting direction, when the user is lifting the artificial leg up from the floor while walking, urging forces urging the artificial leg to kick against the floor can be obtained, and hence it is possible to reduce a kicking force from the walking living body, thereby further reducing burden on the user wearing the artificial leg, and enabling the user to perform smoother walking motion. Further, even when the walking motion demands the angle of the ankle to follow up a road surface and a proper holding force of the ankle joint, e.g. in the case of walking up or down a slope, the demanded follow-up performance and holding force can be ensured by the urging forces of the urging members.

More preferably, the fixed link includes a shock-absorbing member for absorbing shock transmitted between the two limb members.

According to this preferred embodiment, the same advantageous effects as provided by the above parallel linkage can be obtained. More specifically, it is possible to absorb shock transmitted between the two limb members via the fixed link. Therefore, when the artificial joint device is applied e.g. to an artificial leg, it is possible to soften shock transmitted from the artificial leg to a user's living body via the fixed link when the user puts the artificial leg on the floor, to thereby further reduce the burden on the user of the artificial leg.

More preferably, the plurality of expansible links are at least three expansible links.

According to this preferred embodiment, the same advantageous effects as provided by the above parallel linkage can be obtained. More specifically, when the expansible links are each driven e.g. by an actuator for expansion and contraction, it is possible to operate the expansible links to twist the two limb members in respective opposite rotating directions, and realize an automatically controlled artificial joint device having such a twisting capability.

Further preferably, the at least three expansible links are arranged such that connecting portions thereof connected to at least one of the two limb members are not in a line on the at least one of the two limb members, and that a connecting portion of the fixed link is positioned within a polygon defined by the connecting portions of the at least three expansible links as vertexes.

According to this preferred embodiment, the same advantageous effects as provided by the above parallel linkage can be obtained. More specifically, it is possible to make compact in size the automatically controlled artificial joint device capable of twisting the two limb members in the respective opposite rotating directions. Further, a driving force required for causing the twisting motion can be reduced, which contributes to enhancement of operating efficiency.

Further preferably, the artificial joint device further comprises a drive source, actuators each for actuating a corresponding one of the at least three expansible links for expansion and contraction by a driving force supplied from the drive source, and control means for controlling the driving force supplied to the each actuator from the drive source.

According to this preferred embodiment, the same advantageous effects as provided by the above parallel linkage can be obtained. More specifically, it is possible to twist the two limb members in the respective opposite rotating directions. Therefore, when the artificial joint device is applied e.g. to an ankle joint of an artificial leg, it is possible to enable the user to perform twisting of an ankle thereof and smooth turning motion in walking, as well as to realize an automatically controlled artificial leg having such a twisting capability. Further, when the artificial joint device is applied to a joint at the ball of the foot of the artificial leg, the artificial leg enables still smoother turning motion in walking, so that it is possible to approximate the motion of the automatically controlled artificial leg to that of a living leg. Besides, by making the fixed link solid and robust, as described hereinbefore, it is possible to cause the fixed link to bear load from the weight of a user, which enables reduction of the driving forces supplied to the actuators, thereby contributing to reduction of energy consumption by the automatically controlled artificial leg. Similarly, when the artificial joint device is applied to a wrist joint or a joint at a thenar of an artificial arm, it is possible to realize an automatically controlled artificial hand or arm. The use of the artificial joint device makes it possible not only to approximate the motion of the artificial hand or arm to that of a living hand or arm, but also to reduce energy consumption. Further, when the artificial joint device is applied to a limb of a robot, it is also possible to obtain the same effects as described above.

Even more preferably, the actuator is an electric actuator configured to produce regenerative power when the corresponding expansible link is expanded and contracted by an external force, and the artificial joint device further comprises an accumulator for storing the regenerative power produced by the electric actuator.

According to this preferred embodiment, the same advantageous effects as provided by the above parallel linkage can be obtained. Therefore, when the artificial joint device is applied to a prosthetic limb or a limb of a robot, it is possible to reduce both the size of the power supply and running costs, which contributes to reduction of costs of the prosthetic limb or the robot.

Even more preferably, the artificial joint device is used in at least one of an artificial leg and an artificial arm, and further comprises operating will-detecting means for detecting a user's operating will to operate the at least one of the artificial leg and the artificial arm, and the control means controls the actuators according to the sensed operating will.

According to this preferred embodiment, operating will of a user using the artificial leg and/or the artificial arm is detected by the operating will-detecting means, and the actuators are controlled by the control means according to the sensed operating will. In general, the motion of a joint of a living body, particularly the motion of a joint of a limb is complicated, so that when a parallel linkage using actuators is used to imitatively realize the complicated motion, it is impossible to control the parallel linkage directly by an instruction or the like from a user's brain. For this reason, a control system is needed to detect the user's operating will from operations of the user's brain, nerves, and/or muscles and control the parallel linkage according to the sensed operating will. Therefore, the artificial joint device makes it possible to cause the motion of the automatically controlled artificial leg and/or artificial arm to match or conform with a motion intended by the user, thereby enhancing convenience of the artificial leg and/or artificial arm.

Preferably, the parallel linkage comprises an inexpansible movable link extending between the two limb members, and two movable-link joints for connecting opposite ends of the inexpansible movable link to the two limb members, respectively, such that respective angles of the inexpansible movable link with respect to the limb members can be changed in any desired direction.

According to this preferred embodiment, since the opposite ends of the inexpansible movable link are connected to the two limb members, respectively, such that respective angles of the inexpansible movable link with respect to the limb members can be changed in any desired direction, it is possible to maintain a constant distance between the portions of the respective limb members connected to the inexpansible movable link as well as to constrain a superfluous degree of freedom of the parallel linkage and limit unnecessary motion of the same.

Preferably, the artificial joint device is used for a hallux portion, and the parallel linkage includes at least three expansible links extending between the two limb members in an expansible/contractible manner, and a plurality of expansible-link joints respectively connecting opposite ends of the at least three expansible links to the limb members such that respective angles of each expansible link with respect to the limb members can be changed in any desired direction, the artificial joint device further comprising a drive source, actuators each for actuating a corresponding one of the at least three expansible links for expansion and contraction by a driving force supplied from the drive source, and control means for controlling the driving force supplied to the each actuator from the drive source.

Preferably, the artificial joint device is used for a thumb portion, and the parallel linkage includes at least three expansible links extending between the two limb members in an expansible/contractible manner, and a plurality of expansible-link joints respectively connecting opposite ends of the at least three expansible links to the limb members such that respective angles of each expansible link with respect to the limb members can be changed in any desired direction, the artificial joint device further comprising a drive source, actuators each for actuating a corresponding one of the at least three expansible links for expansion and contraction by a driving force supplied from the drive source, and control means for controlling the driving force supplied to the each actuator from the drive source.

According to these preferred embodiments, since the opposite ends of each of the at least three expansible links are respectively connected to the limb members such that respective angles of the expansible link with respect to the limb members can be changed in any desired direction, it is possible to achieve a high degree of freedom of a joint at the ball of the foot (joint to a hallux (big toe)) or a joint at a thenar (joint to a thumb). In addition, since the operations of the actuators actuating the respective expansible links are controlled by the control means, it is possible to realize an automatically controlled joint at the ball of the foot or at the thenar. Therefore, when the artificial joint device is applied to a joint at the ball of the foot (joint to a hallux) of an artificial foot or leg, the motion of the hallux which plays an important role in turning motion of the artificial foot or leg performed during walking, can be approximated to that of a living hallux. Thus, it is possible to approximate the walking motion, including turning motion, of the automatically controlled artificial foot or leg to that of a living foot or leg, thereby enabling smooth walking motion of the artificial foot or leg. Similarly, when the artificial joint device is applied to a joint at a thenar (joint to a thumb) of an artificial hand or arm, it is possible to approximate the degree of freedom in the motion of the automatically controlled artificial hand or arm to that of a living hand or arm. Further, when the artificial joint device is applied to a joint of a limb of a robot, it is possible to obtain the same advantageous effects as described above.

More preferably, the parallel linkage comprises an inexpansible movable link extending between the two limb members, and two movable-link joints for connecting opposite ends of the inexpansible movable link to the two limb members, respectively, such that respective angles of the inexpansible movable link with respect to the limb members can be changed in any desired direction.

According to this preferred embodiment, the same advantageous effects as described above can be obtained. In addition, since it is possible to bend the joint to the hallux or thumb without changing the length of the hallux or thumb, the motion of the hallux or thenar of the automatically controlled prosthetic limb can be further approximated to that of the living hallux or thumb.

More preferably, the control means controls the driving force supplied to the each actuator from the drive source such that a distance between the two limb members is held constant.

According to this preferred embodiment, it is possible to further approximate the motion of the joint to the hallux or thumb of the automatically controlled prosthetic limb to that of the living hallux or thumb without increasing component parts of the prosthetic limb in number.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will now be described in detail with reference to drawings showing preferred embodiments thereof.

Referring first toFIG. 1, there is schematically shown the construction of an artificial leg1in which an artificial joint device2including a parallel linkage according to a first embodiment of the invention is applied to an ankle joint thereof. In the following description, the left and right sides and the front and rear sides as viewed from a user wearing the artificial leg are referred to as the left and right sides and the front and rear sides, respectively (more specifically, the left and right sides as viewed inFIG. 1are referred to as the front and rear sides, respectively, and the front and rear sides as viewed in the same are referred to as the left and right sides, respectively).

As shown in the figure, the artificial leg1is a type attached to an under-knee leg portion of a living body, and used for a right leg. The artificial leg1includes a foot portion3and a leg mounting portion4, the artificial joint device2connecting these portions by a parallel linkage10, and a cover5. The whole of the artificial leg1, including the artificial joint device2, is covered with the cover5, such that it has an appearance generally similar to that of a living leg.

The foot portion3(link mounting portion, limb member) is similar in shape to a living foot, and has a flat upper end face. The leg mounting portion4is comprised of a flat mounting plate4aand a prosthetic liner4b.In attaching the artificial leg1to a living under-knee leg portion, not shown, of the user, the mounting plate4a(link mounting portion, limb member) is connected to the living under-knee leg portion via a fastener, not shown, with the prosthetic liner4binterposed between the under-knee leg portion and the mounting plate4aitself. The prosthetic liner4bis formed e.g. of porous silicon. When the mounting plate4ais connected to the living under-knee leg portion, the prosthetic liner4bdeforms to conform to the under-knee leg portion and combine the under-knee leg portion and the mounting plate4ain a state in which they are kept from direct contact with each other. This makes it possible to reduce unnatural and unpleasant feeling of the user, thereby enhancing his feeling of wearing the artificial leg.

The parallel linkage10includes one fixed link11and four expansible links13. The fixed link11has an upper end thereof fixed to the mounting plate4aand a lower end thereof connected to the foot portion3via a ball joint12(fixed-link joint). This construction enables the fixed link11to pivotally move in any desired direction with respect to the foot portion3. In short, the fixed link11has at least three degrees of freedom.

Each of the four expansible links13has an upper end thereof connected to the mounting plate4avia an upper ball joint14a(expansible-link joint) and a lower end thereof connected to the foot portion3via a lower ball joint14b(expansible-link joint). Each adjacent two of the four expansible links13is arranged such that a space (or distance) between them is progressively reduced either in an upward direction or in a downward direction. More specifically, the right and left expansible links13,13on the front side are arranged with a space therebetween progressively decreased in the upward direction, and the upper ball joints14a,14aat the respective upper ends of the two expansible links13,13are arranged on the lower surface of the mounting plate4aat respective locations close to each other. On the other hand, each two expansible links13,13in the front-rear direction are arranged with a space (distance) therebetween progressively decreased in the downward direction, and the lower ball joints14b,14bat the respective lower ends of the two expansible links13,13are arranged on the flat upper end face of the foot portion3at respective locations close to each other.

Further, as shown inFIG. 2, the four upper ball joints14aconnecting the respective upper ends of the four expansible links13to the mounting plate4aare positioned on the lower surface of the mounting plate4asuch that they are not arranged in a line, and that a connecting portion of the fixed link11via which the fixed link11is connected to the mounting plate4ais located within a quadrilateral defined by the upper ball joints14aas vertexes.

Each of the expansible links13is comprised of upper and lower cylinders13a,13bslidably fitted to each other and a coil spring13creceived within the cylinders13a,13b.The lower cylinder13bis smaller in diameter than the upper cylinder13aand fitted in a bore of the upper cylinder13a.This construction enables the two cylinders13a,13bto slide relative to each other in an axial direction, and thereby enables the expansible link13to axially expand and contract.

Further, the upper cylinder13ahas an upper end thereof closed by a lid, not shown, to which is attached the upper end of the coil spring13c.Similarly, the lower cylinder13bhas a lower end thereof closed by a lid, not shown, to which is attached the lower end of the coil spring13c.According to this construction, when the expansible link13expands to a larger length than a predetermined reference length, the coil spring13c(urging member) is pulled and stretched by the motion of the expansible link13, to urge the expansible link13in a contracting direction. On the other hand, when the expansible link13contracts to a smaller length than the predetermined reference length, the coil spring13cis compressed by the motion of the expansible link13, to urge the expansible link13in an expanding direction.

The operation of the artificial leg1constructed as above will be described with reference toFIGS. 3A to 7B. It should be noted that in the artificial leg1shown in the figures, a shoe6is fitted on the foot portion3, and the cover5and the prosthetic liner4bare omitted for clarity. Further, in the figures, the living under-knee leg portion to which the artificial leg1is attached is omitted from illustration.

First, in a state detached from the living under-knee leg portion, the artificial leg1is held in a substantially erected state by the urging force of the coil spring13cwithin each expansible link13as shown inFIGS. 3A,3B and4. As illustrated inFIG. 4, assuming that a front expansible link13performs pivotal motion freely about the corresponding lower ball joint14b,the center of the upper ball joint14aat the upper end of the expansible link13may be expected to move in a circular arc shown by a broken line, but actually, it moves in a circular arc shown by a solid line, more specifically along a circular arc drawn with the lower ball joint12of the fixed link11as its center. Accordingly, the front expansible link13is compressed when the artificial leg1tilts forward from a position shown inFIG. 4, and expanded when the artificial leg1tilts backward. In these operations, since the upper and lower ends of the expansible link13are connected to the mounting plate4aand the foot portion3, respectively, via the upper and lower ball joints14a,14b,no bending stress is applied to the front expansible links13, but only compressive load and/or tensile load are applied to the same.

Similarly to the front expansible link13, assuming that a rear expansible link13performs pivotal motion freely about the corresponding lower ball joint14b,the center of the upper ball joint14aat the upper end of the expansible link13may be expected to move in a circular arc shown by a broken line, but actually, it moves in a circular arc shown by a solid line, more specifically along a circular arc drawn with the lower ball joint12of the fixed link11as its center. Accordingly, the rear expansible link13is also compressed when the artificial leg1tilts forward from the position shown inFIG. 4, and expanded when the artificial leg1tilts backward. In these operations, for the same reason as described above, no bending stress is applied to the rear expansible links13, but only compressive load and/or tensile load are applied to the same.

Therefore, when the user wearing the artificial leg1at the living under-knee leg portion tilts the under-knee leg portion forward while walking, as shown inFIG. 5A, the four expansible links13are all compressed as described above. At this time point, since the lower ball joints14bof the four expansible links13are positioned at the respective locations forward of the ball joint12of the fixed link11, the urging forces of the four coil springs13cact to cause the foot portion3to pivotally move toward a floor about the ball joint12of the fixed link11, while reaction forces from the floor act to push the living under-knee leg portion in an obliquely upward and forward direction. As a result, motion of kicking against the floor by the artificial leg1is promoted, which enables nimbler and smoother walking motion.

On the other hand, when the user tilts the under-knee leg portion backward while walking, as shown inFIG. 5B, the four expansible links13are all expanded as described above. At this time point, since the lower ball joints14bof the four expansible links13are positioned as described above, the urging forces of the four coil springs13cact to cause the fixed link11to pivotally move forward about the ball joint12thereof. As a result, motion of moving the knee forward is promoted, which enables nimbler and smoother walking motion.

Further, as shown inFIG. 6A, when the under-knee leg portion is tilted leftward, two expansible links13on the left side are both compressed, while two expansible links13on the right side are both expanded. This occurs because the center of the upper ball joint14aof each expansible link13moves in a circular arc about the lower ball joint12at the lower end of the fixed link11as described above. At this time point, the urging forces of the four coil springs13cact to cause the fixed link11to pivotally move rightward about the ball joint12thereof. In short, the urging forces act to return the fixed link11to the state shown inFIGS. 3A,3B.

On the other hand, as shown inFIG. 6B, when the under-knee leg portion is tilted rightward, two expansible links13on the right side are both compressed, while two expansible links13on the left side are both expanded. At this time point, the urging forces of the four coil springs13cact to cause the fixed link11to pivotally move leftward about the ball joint12thereof. In short, the urging forces act to return the fixed link11to the state shown inFIGS. 3A,3B.

Further, when the under-knee leg portion is tilted leftward and twisted about the foot portion3as shown inFIGS. 7A,7B so as to turn left, the urging forces of the four coil springs13cact to return the same to the state shown inFIGS. 3A,3B while twisting the fixed link11rightward.

According to the above parallel linkage10, the upper end of the fixed link11is fixed to the mounting plate4a.Therefore, by making the fixed link11solid and robust, it is possible to bear most of the user's weight acting on the mounting plate4aor most of the reaction force that the foot portion3receives from the floor. In addition, since each of the four expansible links13has the upper and lower ends thereof connected to the mounting plate4aand the foot portion3via the ball joints14a,14b,respectively, such that the angle thereof with respect to the mounting plate4aor the foot portion3can be changed in any desired direction, no bending stress is applied to the expansible links13, but only compressive load and/or tensile load are applied to the same. This makes it possible to use expansible links13having relatively low strength and rigidity, thereby reducing the weight of the parallel linkage10. Further, the fixed link11has the lower end thereof connected to the foot portion3via the ball joint12such that the angle thereof with respect to the foot portion3can be changed in any desired direction, which ensures a high degree of freedom in the angle of relative motion between the living under-knee leg portion and the foot portion3, to thereby enable e.g. twisting motion of the ankle joint.

Further, according to the parallel linkage10, each of the coil springs13curges the corresponding expansible link13in a direction opposite to the expanding direction or the contracting direction of the spring13c,which makes it possible to reduce shock transmitted to the living body via the expansible links13. Furthermore, as described hereinabove, when the user tilts the under-knee leg portion forward while walking, the urging forces of the coil springs13cpromote the motion of kicking against the floor by the foot portion3, and when the user tilts the under-knee leg portion backward, the urging forces of the coil springs13cpromote the motion of moving the knee forward, so that walking motion can be performed more nimbly and smoothly. Moreover, even when the walking motion demands the angle of the ankle to follow up a road surface and a proper holding force of the ankle joint, e.g. in the case of walking up or down a slope, the demanded follow-up performance and holding force can be ensured by the urging forces of the coil springs13c.

Therefore, the artificial joint device2using the parallel linkage10constructed as above makes it possible to enhance the degree of freedom in the angle of motion of the ankle joint to a level similar to that of an ankle joint of a living leg, which has been unattainable by the artificial joint device of the conventional artificial leg, to thereby enable the artificial leg1to smoothly perform turning motion and the like. Moreover, differently from an artificial joint device of a serial linkage type conventionally used e.g. in a robot, the artificial joint device2can realized by using the parallel linkage10which is simpler, less expensive, and smaller in size than the serial linkage, without using power supply or electric motor.

Although in the parallel linkage10of the above first embodiment, the lower end of the fixed link11and the upper and lower ends of each of the expansible links13are all connected to the foot portion3or the mounting plate4avia the respective ball joints12,14a,14b,this is not limitative, but joints for use in connecting the links11,13to the foot portion3or the mounting plate4amay be each implemented by any suitable joint which allows the link11or13to be connected to the foot portion3or the mounting plate4asuch that the angle thereof with respect to the foot portion3or the mounting plate4acan be changed in any desired direction. In short, any suitable joint having at least three degrees of freedom may be employed. For instance, joints, such as universal joints, which can perform spherical motion may be used. Further, although in the first embodiment, the coil spring13cis used as urging means for urging each of the expansible links13in opposite directions to respective expanding and contracting directions of the expansible link13, when the expansible link13expands and contracts, this is not limitative, but any urging means may be used which is capable of urging the expansible link13in an opposite direction to at least one of the expanding and contracting directions of the expansible link13. For instance, fluid springs, such as air springs, may be used as the urging means. Further, the number of the expansible links13is not limited to four, but any plural number of the expansible links13may be used.

Next, an artificial joint device2according to a second embodiment of the present invention will be described with reference toFIG. 8. It should be noted that in the following description, component parts and elements similar or equivalent to those of the first embodiment are designated by identical reference numerals, and detailed description thereof is omitted when deemed appropriate. As shown in the figure, the artificial joint device2of the present embodiment is distinguished from the artificial joint device2of the first embodiment only by having a different fixed link11.

More specifically, the fixed link11is expansible, and includes a cylinder11a,a rod11band a coil spring11c(shock-absorbing member). The cylinder11ahas an upper end fixed to a mounting plate4aand an open lower end. The rod11bis fitted in a bore of the cylinder11asuch that the rod11bcan reciprocate within the bore, and has a lower end thereof connected to a foot portion3via a ball joint12.

Further, the rod11bhas a flange11dformed on a portion upward of a connecting portion thereof via which the rod11bis connected to the ball joint12. The coil spring11cis interposed between the flange11dand the cylinder11ain a state wound around the rod11b,for urging the rod11band the cylinder11ain a direction for expanding a space between the flange11dand the cylinder11a.

According to the artificial joint device2constructed as above, it is possible to use the urging force of the coil spring11cto reduce a shock transmitted to the living body of a user wearing an artificial leg1via the fixed link11by a reaction force from the floor when the user puts the artificial leg1onto the floor while walking. Further, this construction makes it possible to reduce a burden on the user wearing the artificial leg1including the artificial joint device2, thereby further improving the user's feeling of wearing or using the artificial leg1.

Although in the above second embodiment, the coil spring11cis used as the shock-absorbing member for reducing the shock transmitted to the living body via the fixed link11, this is not limitative, but the shock-absorbing member may be implemented by any suitable means having a shock-absorbing property. For instance, a fluid spring, such as an air spring, or a synthetic rubber may be employed.

Next, an artificial joint device according to a third embodiment of the present invention will be described with reference toFIGS. 9A to 11B. The artificial joint device of the present embodiment is applied to an artificial joint device for an ankle joint of an electrically controlled artificial leg and an artificial joint device for a joint at the ball of the foot. First, a description is given of the artificial joint device2for the ankle joint. This artificial joint device2is distinguished from the artificial joint device2of the first embodiment in that it includes electrically-driven expansible links13and a control system20for controlling the expansible links13.

More specifically, as shown inFIGS. 10 and 11A,11B, each of the expansible links13includes an electrically-driven artificial muscle13dreceived in two cylinders13a,13b.The electrically-driven artificial muscle13d(actuator) is formed by a polymer actuator composed e.g. of polyacrylonitrile. The electrically-driven artificial muscle13dexpands and contracts in response to input signals to thereby expand and contract the expansible link13. Further, the electrically-driven artificial muscle13dis a power regenerative type which produces regenerative electric power by being pressurized.

The control system20includes a controller21(control means), a power supply22(drive source), and a capacitor23(accumulator). The electrically-driven artificial muscle13dis connected to the power supply22and the capacitor23, via the controller21. The power supply22is formed e.g. by a fuel cell. Further, an implant chip24(operating will-detecting means) and a joint position sensor25are connected to the controller21.

The implant chip24is implanted in a brain8of a user7of an artificial leg1. The implant chip24detects an instruction from the brain8, or more specifically an instruction representative of an operating will of the user7to operate the artificial leg1, and delivers a signal indicative of the sensed driver's operating will to the controller21. Further, the joint position sensor25detects an angle position of each of the electrically-driven artificial muscles13dand delivers a signal indicative of the sensed angle position to the controller21.

The controller21is formed by a microcomputer, and controls electric power supplied to the electrically-driven artificial muscles13dfrom the power supply22or the capacitor23, in response to the detection signals from the implant chip24and the joint position sensor25(seeFIG. 11A). Further, when the electrically-driven artificial muscles13dare producing regenerative power by being pressurized, the controller21charges the capacitor23with the produced regenerative power and at the same time controls the amount of the regenerative power (seeFIG. 11B).

Next, a description will be given of the artificial joint device2A for the joint at the ball of the foot. The artificial joint device2A includes a foot portion3, a hallux (big toe) portion16and a parallel linkage15. The parallel linkage15is comprised of three expansible links17and a movable link19.

The hallux portion16is comprised of two hallux members16a,16b(limb members) and a rotary joint16cfor connecting the two hallux members16a,16bsuch that they are pivotable with respect to each other.

The expansible links17are each constructed similarly to the electrically-driven expansible link13described above, except that the former is smaller in size than the latter. More specifically, as shown inFIG. 10, each of the expansible links17incorporates an electrically-driven artificial muscle17d(actuator) connected to the controller21, and has its expanding/contracting operation controlled by the controller21. Further, each of the expansible links17has opposite ends thereof connected to the foot portion3and the hallux member16bof the hallux portion16, respectively, via respective ball joints18,18(joints for the expansible link).

The movable link19is inexpansible, and has opposite ends thereof connected to the foot portion3and the hallux member16bof the hallux portion16, respectively, via respective ball joints19a,19a(joints for the movable link). Thus, the distance between connecting portions of the foot portion3and the hallux member16bvia which the foot portion3and the hallux member16bare connected to the movable link19, respectively, is held constant even when the expansible links17expand or contract.

According to the artificial joint device2for an ankle joint, constructed as above, the electrically-driven artificial muscle13dincorporated in each of the expansible links13can be controlled by the controller21in response to the detection signals from the implant chip24and the joint position sensor25, which makes it possible to cause the motion of the electrically controlled parallel linkage10, which is difficult to control directly by an instruction or the like from the brain of the user7, to match (or conform with) a motion intended by the user7. In the thus-controlled motion, the angle of motion of the artificial joint device2of the artificial leg1can be changed by the parallel linkage10with a high degree of freedom. In particular, since the respective upper ball joints14aof the expansible links13are arranged such that the ball joints14aare not positioned in a line on the mounting plate4aand that the connecting portion of the fixed link11via which the fixed link11connected to the mounting plate4ais positioned within a quadrilateral defined by the upper ball joints14aas vertexes, it is possible not only to twist the artificial joint device2as illustrated inFIGS. 7A,7B, but also to make the expansible links13and hence the artificial joint device2, compact in size.

Similarly to the artificial joint device2for an ankle joint, the artificial joint device2A for the joint at the ball of the foot is capable of controlling the electrically-driven artificial muscle17dincorporated in each of the expansible links17by the controller21in response to the detection signals from the implant24and the joint position sensor25, so that it is possible to cause the motion of the electrically controlled parallel linkage15, which is difficult to control directly by an instruction or the like from the brain of the user7, to match (or conform with) a motion intended by the user7. In the motion, the parallel linkage15makes it possible to achieve a high degree of freedom in changing the angle of motion of the joint at the ball of the foot of the artificial leg1, whereby the motion of the hallux portion16, which plays an important role in turning motion of the artificial leg1during walking, can be approximated to that of the hallux of a living foot. Further, since the hallux member16bof the hallux portion16is connected to the foot portion3via the inexpansible movable link19, it is possible to bend the joint at the ball of the foot almost without changing the length of the hallux when the parallel linkage15is operated, to thereby further approximate the motion of the joint at the ball of the foot to that of the joint at the ball of the living foot. Thus, the walking motion, including the turning motion, by the automatically controlled artificial leg1can be approximated to that of a living leg, thereby enabling smooth walking motion.

Further, since most of the load applied to the artificial leg1can be supported by the fixed link11, it is possible to reduce the respective driving forces of the electrically-driven artificial muscles13dfor driving the corresponding expansible links13, and reduce the weight of the expansible links13. In addition, it is possible to produce regenerative power by each artificial muscle13dwhen the corresponding expansible link13is compressed, so that reduction of both power consumption and the size of the power supply can be achieved. This makes it possible to reduce not only running costs but also the size of the device itself.

Although in the above third embodiment, the implant chip24is used as detection means for detecting the signal indicative of the user's operating will, this is not limitative, but any suitable means capable of detecting a user's operating will may be employed as the detection means. For instance, it is possible to use a sensor for detecting changes in a potential of the nervous system, a sensor for detecting the movement of muscles, a sensor for detecting a user's voice, etc.

Further, although in the third embodiment, the movable link19is used as means for preventing the length of the hallux from being changed during bending motion of the joint at the ball of the foot, the movable link19may be omitted, and expansion and contraction of the expansible links17may be controlled by the controller21to hold the length of the hallux almost constant during bending motion of the joint at the ball of the foot. This makes it possible to further approximate the bending motion of the joint at the ball of the foot of the present embodiment to that of the joint at the ball of the living foot.

Furthermore, although in the third embodiment, the capacitor23is used as an accumulator for storing regenerative power produced by the electrically-driven artificial muscles13d,this is not limitative, but any suitable means, such as a battery, which is capable of storing the produced regenerative power, may be used as the accumulator.

Moreover, although in the third embodiment, the artificial muscle13dis used as an actuator for expanding and contracting the corresponding expansible link13, this is not limitative, but any suitable means capable of expanding and contracting the expansible link13may be used as the actuator. For instance, as shown inFIGS. 12A to 12C, a DC linear motor30may be used as the actuator for expanding and contracting the expansible link13.

As shown inFIG. 12C, the DC linear motor30includes a stator31and a mover32movable with respect to the stator31. The mover32includes a position sensor, and is connected to the controller21. Further, as shown inFIGS. 12A,12B, an expansible link13has the stator31as an arm and the mover32installed therein, and further includes a slider33slidable with respect to the stator31, and ball joints14a,14battached to respective ends of the stator31and the slider33on opposite sides.

The controller21controls the slider33in response to a signal from the position sensor of the mover32within the slider33such that the slider33linearly moves with respect to the stator31, whereby the expansible link13is controlled for expansion and contraction. If the expansible links13each driven by the DC linear motor30described above are used in the parallel linkage10, it is possible to obtain the same advantageous effects as provided by the parallel linkage10of the third embodiment.

Further, when power regeneration by the actuator is not needed, the actuator may be implemented e.g. by an artificial muscle formed of a magnetic shape-memory alloy or a pneumatic-type artificial muscle.

Further, in the third embodiment, the fixed link11may be constructed similarly to the fixed link11in the second embodiment as shown inFIG. 13. More specifically, as shown in the figure, the fixed link11is expansible, and includes a cylinder11a,a rod11band a coil spring11c.According to this variation of the parallel linkage10according to the third embodiment, the same advantageous effects as provided by the parallel linkage10of the second embodiment can be obtained.

Next, an artificial joint device according to a fourth embodiment will be described with reference toFIG. 14. As shown in the figure, the artificial joint device of the present embodiment is applied to an artificial joint device for a wrist joint and a joint at a thenar of an artificial arm. The artificial joint device2B for the wrist joint of the artificial arm40is comprised of a hand portion9(limb member), a mounting plate4a,and a parallel linkage10connecting the hand portion9and the mounting plate4a.The parallel linkage10is an electrically controlled type similar to the parallel linkage10of the third embodiment, and has its operation controlled by a control system similar to the control system20described hereinabove. In short, the artificial joint device2B is constructed similarly to the artificial joint device2for an ankle joint according to the third embodiment except that the foot portion3is replaced by the hand portion9.

Therefore, the artificial joint device2B for a wrist joint can provide the same advantageous effects as obtained by the artificial joint device2of the third embodiment. More specifically, the artificial joint device2B makes it possible to cause the motion of the electrically controlled parallel linkage10, which is difficult to control directly by an instruction or the like from the brain of a user, to match (or conform with) a motion intended by the user. In the motion, it is possible to change the angle of motion of the artificial joint device2B of the artificial arm40by the parallel linkage10, with a high degree of freedom.

An artificial joint device2C for the joint at a thenar is comprised of a hand portion9, a thumb portion16, and a parallel linkage15connecting the hand portion9and the thumb portion16. The artificial joint device2C is constructed similarly to the artificial joint device2for the joint at the ball of the foot according to the third embodiment except that the foot portion3is replaced by the hand portion9and that the thumb portion16is slightly different in construction from the hallux portion16. Therefore, the artificial joint device2C for the joint at a thenar can provide the same advantageous effects as obtained by the artificial joint device2A for the joint at the ball of the foot according to the third embodiment. More specifically, the artificial joint device2C makes it possible to cause the motion of the electrically controlled parallel linkage15, which is difficult to control directly by an instruction or the like from the brain of a user, to match (or conform with) a motion intended by the user. In the motion, the parallel linkage15makes it possible to achieve a high degree of freedom in changing the angle of motion of the joint at the thenar, and hence the motion of the thumb portion16, which plays an important role in grasping motion, can be approximated to that of the thumb of a living hand.

Although in the above third and fourth embodiments, the artificial joint device of the invention is applied to the artificial leg and the artificial arm, this is not limitative, but the artificial joint device is applicable to an artificial limb of a robot, a manipulator, and the like.

It is further understood by those skilled in the art that the foregoing are preferred embodiments of the invention, and that various changes and modifications may be made without departing from the spirit and scope thereof.