US20230310181A1 - Knee joint - Google Patents

Abstract

A knee joint that is capable of widening a moveable range, and that has good energy efficiency and is small and lightweight is described. Also described is a knee joint that is of an active type, but comparatively inexpensive. A drive section moves a driven member. An elastic member is arranged between the driven member and a linear motion member. The linear motion member elastically moves in at least one direction, in accordance with movement of the driven member, by way of the elastic member. A crank mechanism can realize bending and extension of the knee joint by converting linear motion of the linear motion member to rotational motion.

Description

BACKGROUNDTechnical Field
• The present disclosure relates to a knee joint used in a prosthetic leg.
Description of the Related Art
• Generally, a prosthetic leg is made up of a socket that is fixed to a section of a leg, a knee joint that is connected to a lower end of the socket, and a grounding part that is connected to a lower end of the knee joint. The knee joint, similar to a human knee joint, is capable of extending and bending within a specified angular range.
• As a knee joint drive method, three methods exist, namely a passive method, an electronic control method, and an active method. With a passive method, the wearer moves the prosthetic leg, and the knee joint passively bends/extends using a damper of a hydraulic pressure cylinder or pneumatic cylinder and spring force, etc., in accordance with movement of the prosthetic leg. With an electronic control method, movement resistance to bending and extension of the knee joint is adjusted using electronic control, and operation of the knee joint can be improved. One example of an electronic control method knee joint is shown in Japanese patent laid-open No. 2004-167106. Also, with an active method, by actively controlling bending angle of the knee joint using a motor, knee joint movement for operations such as going up and down stairs is supported.
• However, a conventional active method knee joint has a problem in that not only is cost high due to its complicated structure, it is also likely that the wearer will become tired due to the weight. In particular, with a conventional active method knee joint, it is necessary to always operate a motor that is mounted on the knee joint, and since energy efficiency is not good, a large capacity battery is required, which tends to make the knee joint large and heavy.
• On the other hand, an active method knee joint that moves a knee joint by converting linear motion from a series elastic actuator to rotational movement using a pulley is disclosed in Elliott J. Rouse, Luke M. Mooney and Hugh M. Herr, “Clutchable series-elastic actuator: Implications for prosthetic knee design,” Oct. 9, 2014, doi: 10.1177/0278364914545673, The International Journal of Robotics Research, November 2014 vol. 33 no. 13 1611-1625. With this technology, walking energy is utilized by using a spring of a series elastic actuator, and high energy efficiency is obtained compared to energy efficiency of a conventional active method knee joint. However, with this technology, in order to convert linear motion of the series elastic actuator to rotational motion of the knee, it results in a mechanism that rotates the knee by way of a belt having two pulleys fixed to elastic elements that move linearly. In order to prevent interference between the elastic elements that move linearly and the knee, it is necessary to arrange the belt and pulleys at a side surface of the knee joint. If this is done, then a need arises to use two belts in a single knee joint, in order to maintain balance. Accordingly, with this technology there is a problem that the mechanism becomes extremely complicated, and there are a lot of components. If an angle through which the knee joint can be moved (moveable range) is widened, then the belt and the pulley become large in size, and the knee joint becomes difficult to use due to the size and weight. Also, since a belt for moving the pulleys has a problem from a point of view of durability, there is a tendency for cost to increase easily because of maintenance and replacement of the belt.
• Also, a structure for rotatably attaching a knee member to an upper end of a lower limb member, and attaching a foot member to a lower end of the lower limb member, is described in International patent application 2004/017872. A projecting member is integrally formed with a side section of the knee member, and a linear actuator is attached between this projecting member and a lower part of a lower limb member. With this technology it is possible to supplement rotational movement of the knee member using drive force of this linear actuator. However, with this technology, because of the structure where the linear actuator is directly connected to the knee member without a reduction gear, there is problem in that a high load acts on the linear actuator in order to acquire high driving torque.
BRIEF SUMMARY
• The present disclosure has been conceived based on the previously described situation. The present disclosure provides a knee joint that is capable of widening a moveable range, and has good energy efficiency and is small and lightweight.
• Apparatus for solving the above described problem can be described as in the following aspects.
• (Aspect 1)
• A knee joint, comprising a drive section, a series elastic mechanism, and a crank mechanism, wherein the series elastic mechanism comprises a driven member, an elastic member, and a linear motion member, the drive section is configured to move the driven member, the elastic member is arranged between the driven member and the linear motion member, the linear motion member is configured to elastically move in at least one direction, in accordance with movement of the driven member, by way of the elastic member, and the crank mechanism is configured to convert linear motion of the linear motion member to rotational motion.
• (Aspect 2)
• The knee joint ofaspect 1, further comprising an upper connection section for connecting a socket and the knee joint, wherein the crank mechanism is configured to cause rotational movement of the upper connection section in forward and backward directions.
• (Aspect 3)
• The knee joint ofaspect 1 and/oraspect 2, further comprising a frame, wherein the linear motion member is capable of movement in at least one direction with respect to the frame.
• (Aspect 4)
• The knee joint ofaspect 1 and/oraspect 2, further comprising a frame, wherein a rotational shaft of the crank mechanism is supported by the frame.
• (Aspect 5)
• The knee joint of any one ofaspect 1 toaspect 4, wherein the drive section comprises a motor, a speed change mechanism, and a ball screw, and wherein the motor is configured to cause rotation of the ball screw in forward and backward directions by way of the speed change mechanism, and the driven member is configured to move linearly in response to rotation of the ball screw.
• (Aspect 6)
• The knee joint of any one ofaspect 1 toaspect 5, wherein the linear motion member comprises a first contact section and a second contact section that are arranged facing each other, either side of the driven member, the elastic member comprises a first spring and a second spring, the first spring is arranged between the first contact section and the driven member, and the second spring is arranged between the second contact section and the driven member.
• (Aspect 7)
• A prosthetic leg provided with the knee joint of any one ofaspect 1 toaspect 6.
• According to the present disclosure, it is possible to provide a knee joint that has good energy efficiency, is small and light, and is capable of broadening movement range. Also, according to the present disclosure, it is possible to provide a knee joint that is of an active type, but comparatively inexpensive.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
• FIG.1 is a perspective drawing of a knee joint (bending angle=0° of one embodiment of the present disclosure, in a state with a cover removed.
• FIG.2 is a front view ofFIG.1.
• FIG.3 is a left side view ofFIG.2.
• FIG.4 is a plan view ofFIG.2.
• FIG.5 is a cross sectional view taken along line A-A inFIG.3.
• FIG.6 is a perspective view of the knee joint ofFIG.1 in a state where the cover is attached.
• FIG.7 is a front view ofFIG.6.
• FIG.8 is a left side view ofFIG.7.
• FIG.9 is a plan view ofFIG.7.
• FIG.10 is a cross sectional view taken along line A-A inFIG.8.
• FIG.11 is a perspective view of the knee joint ofFIG.1, in a state where the bending angle is 60°.
• FIG.12 is a front view ofFIG.11.
• FIG.13 is a left side view ofFIG.12.
• FIG.14 is a plan view ofFIG.12.
• FIG.15 is a cross sectional view taken along line A-A inFIG.13.
• FIG.16 is a perspective view of the knee joint ofFIG.1, in a state where the bending angle is 120°.
• FIG.17 is a front view ofFIG.16.
• FIG.18 is a left side view ofFIG.17.
• FIG.19 is a plan view ofFIG.17.
• FIG.20 is a cross sectional view taken along line A-A inFIG.18.
• FIG.21 is a schematic explanatory drawing showing an example of having constructed a prosthetic leg using the knee joint ofFIG.1.
• FIG.22 is an explanatory drawing for describing operation of the prosthetic leg ofFIG.21.
• FIG.23 is an explanatory drawing for describing operation of a crank mechanism of the knee joint ofFIG.1.
• FIG.24 is a schematic explanatory drawings of the crank mechanism ofFIG.23.
• FIG.25 is a graph showing one example of characteristics of the crank mechanism ofFIG.24, with the horizontal axis showing knee angle (degrees) and the vertical axis showing reduction ratio.
• FIG.26 is a graph showing change in knee angle at the time of walking, with the horizontal axis showing time (arbitrary units) and the vertical axis showing knee angle (degrees).
• FIG.27 is an explanatory drawing showing an example where offset amount of a series elastic mechanism with respect to a rotation shaft of a crank mechanism has changed.
• FIG.28 is a graph showing a characteristic example of the crank mechanism ofFIG.27 overlapped on the characteristic example ofFIG.25, with the horizontal axis showing knee angle (degrees) and the vertical axis showing reduction ratio.
DETAILED DESCRIPTION
• A knee joint of one embodiment of the present disclosure will be described in the following with reference to the attached drawings (FIG.1 toFIG.10). It should be noted that among these drawings,FIG.1 toFIG.5 show a state where a cover51 (described later) of aframe5 has been removed, whileFIG.6 toFIG.10 show a state where thecover51 has been attached.
• Theknee joint100 of this embodiment can constitute a prosthetic leg by combining asocket200 and afoot section300, as shown inFIG.21 (described later). The structure of theknee joint100 of this embodiment will be described in the following.
Structure of This Embodiment
• Theknee joint100 of this embodiment comprises adrive section1, a serieselastic mechanism2, and acrank mechanism3. This knee joint100 further comprises anupper connection section4, aframe5, and alower connection section6.
• (Drive Section)
• Thedrive section1 comprises amotor11, aspeed change mechanism12, and a ball screw13 (refer toFIG.5) Themotor11 is configured to cause forward and backward rotation of theball screw13 by way of thespeed change mechanism12. Thedrive section1 of this embodiment is provided with a battery (not illustrated), and it is possible to drive themotor11 using electrical power supplied from this battery. However, it is also possible to have a configuration whereby themotor11 is driven using an external power supply (for example, a commercial power supply). Also, thedrive section1 is provided with sensors (not illustrated) that detect rotation angle of thecrank mechanism3 and load on themotor11, and it is possible to control torque and rotation angle of themotor11 in accordance with outputs of these sensors. Themotor11,speed change mechanism12, and ball screw13 of this embodiment are supported by theframe5 via appropriate attachment members or shaft bearings.
• (Series Elastic Mechanism)
• The serieselastic mechanism2 comprises a drivenmember21, anelastic member22, and alinear motion member23. The serieselastic mechanism2 of this embodiment also comprises aguide shaft24 for guiding the drivenmember21, and first andsecond contact sections231 and232 of thelinear motion member23.
• The drivenmember21 is configured to be moved along the guide shaft24 (in the vertical direction inFIG.1) by drive force of thedrive section1. More specifically, the drivenmember21 of the serieselastic mechanism2 of this embodiment is configured to reciprocate in a linear direction in response to rotation of theball screw13 of thedrive section1.
• Theelastic member22 is arranged between the drivenmember21 and thelinear motion member23. More specifically, theelastic member22 of this embodiment comprises twofirst springs221 and two second springs222 (refer toFIG.1 andFIG.3). Thefirst springs221 are arranged between the first contact section231 (described later) of thelinear motion member23 and the drivenmember21, but in a state of not being fixed to these members. Thesecond springs222 are arranged between the second contact section232 (described later) of thelinear motion member23 and the drivenmember21, but in a state of not being fixed to these members.
• Thelinear motion member23 is configured to elastically move in at least one direction, in accordance with movement of the drivenmember21, by way of theelastic member22. More specifically, as was mentioned previously, thelinear motion member23 of this embodiment is provided with afirst contact section231 and asecond contact section232 that are arranged facing each other either side of the drivenmember21, andlinear motion rods233. Also, thefirst contact section231 and thesecond contact section232 are linked by struts234 (refer toFIG.3). Eachstrut234 penetrates through a drivenmember21, and relative movement is possible between thestrut234 and the drivenmember21. Further, eachstrut234 is arranged in a state respectively passing through the inside of afirst spring221 and asecond spring222 of theelastic member22. With this example, bottom ends of thelinear motion rods233 and upper ends of thestruts234 are connected, and these parts constitute an integrated component.
• There are twoguide shafts24 in this embodiment, and they are respectively arranged so as to connect anupper base52 and a lower base53 (described later) of the frame5 (refer toFIG.2). The twoguide shafts24 are not fixed to the drivenmember21, thefirst contact section231, and thesecond contact section232, and in this way it is possible for the drivenmember21, thefirst contact section231, and thesecond contact section232 to move along an extending direction of the guide shafts24 (that is, in the vertical direction inFIG.2).
• With this embodiment, thelinear motion rods233 of thelinear motion member23 penetrate through theupper base52 of theframe5 and are fixed to an upper surface of the first contact section231 (refer toFIG.2 andFIG.3), and reciprocate along the extending direction of the guide shafts24 (that is, the vertical direction inFIG.1) in accordance with movement of thefirst contact section231 and thesecond contact section232.
• (Crank Mechanism)
• Thecrank mechanism3 is configured to convert linear motion of thelinear motion member23 to rotational motion. Thecrank mechanism3 of this embodiment comprises a connectingrod31, anarm member32, and arotation shaft33.
• One end of the connectingrod31 is pin connected to the upper end of thelinear motion rods233 of thelinear motion member23 so as to enable mutual rotation.
• Thearm member32 is pin connected to the other end of the connectingrod31 so as to enable mutual rotation. Also, thearm member32 is made capable of swinging with therotation shaft33 as a center. Theupper connection section4 is attached to an upper part of thearm member32.
• With this embodiment, therotation shaft33 is attached to the cover51 (described later) of theframe5, and relative position between therotation shaft33 and theframe5 is fixed.
• (Upper Connection Section)
• Theupper connection section4 is for connecting a socket200 (refer toFIG.21 which will be described later) and theknee joint100. Theupper connection section4 realizes extension and bending operations of the prosthetic leg by rotational movement in forward and backward directions using thecrank mechanism3. Theupper connection section4 is also called a pyramid connector, and it is possible to connect to thesocket200 using an existing method.
• (Frame)
• Theframe5 of this embodiment comprises the cover51 (refer toFIG.6 toFIG.10), theupper base52, and thelower base53. With this embodiment, thelinear motion member23 is made capable of movement in at least one direction with respect to the upper andlower bases52 and53 of the frame5 (specifically, the vertical direction inFIG.1). Also, with this embodiment, as was mentioned earlier, therotation shaft33 of thecrank mechanism3 is supported in a state capable of rotation by thecover51 of theframe5. Further, theupper base52 and thelower base53 are respectively fixed with respect to thecover51, so that there is no relative movement.
• (Lower Connection Section)
• Thelower connection section6 is for connecting a foot section300 (refer toFIG.21, which will be described later) and theknee joint100. Thelower connection section6 is fixed to thelower base53 of theframe5. Thelower connection section6 is also called a pyramid connector, and it is possible to connect to thefoot section300 using an existing method.
Operation of This Embodiment
• Next, operation of theknee joint100 of this embodiment will be described with further reference toFIG.11 toFIG.22.
• (Knee Joint Angle Adjustment Operation . . . 0° to 60°)
• In the description of this embodiment, the bending state shown inFIG.1 is defined as the angle of the knee joint being 0°. Operation to bend the bending angle of the knee joint from this state to 60° will be described in the following.
• First, themotor11 of thedrive section1 is made to rotate. If this is done, theball screw13 is rotated by way of thespeed change mechanism12, and the drivenmember21 of the serieselastic mechanism2 moves in one direction (with this example, the downward direction inFIG.1).
• Once this happens, the drivenmember21 applies compression force to thesecond spring222 of theelastic member22, and thelinear motion member23 is moved in one direction (with this example, the downward direction inFIG.1), by way of this spring. If thelinear motion member23 is lowered by spring force, the connectingrod31 of thecrank mechanism3 is lowered, and as a result of that lowering thearm member32 rotates with therotation shaft33 as a center (refer toFIG.11 toFIG.15). In this way it is possible to cause theupper connection section4 to rotate by a desired angle. A knee angle of a person walking repeatedly changes from 0° (extended state) to 60° (bent state). Accordingly, after knee bending to 60° themotor11 is reverse rotated, and the knee returns to the 0° extended state due to the application of compression force to thefirst spring221.
• (Knee Joint Angle Adjustment Operation . . . 60° to 120°)
• Operation from a knee angle of 60° to 120° is operation at the time when the user is seated, sitting in the seiza style (sitting on their legs, or kneeling on the floor). At the time of sitting, in particular, the motor is not operated, but in the case of standing from a seated state, it is possible to provide assistance by operating the motor.
• An example of the knee joint having been bent beyond 60° is shown inFIG.16 toFIG.20. Similar to the previous description, it is possible to cause bending of the knee joint up to about 120° (ideally up to about 140°) by further rotating thearm member32 of thecrank mechanism3.
• By causing reverse rotation of themotor11 of thedrive section1, it is possible to return the bending angle of the knee joint to the initial state)(angle=0°.
• With this embodiment, it is possible to dynamically change bending angle of the knee joint100 by appropriately controlling torque, rotation speed, or rotation angle of themotor11. With usage of the prosthetic leg, for example, when climbing stairs or getting up from a chair, it is possible to support actions of the prosthetic leg user (operations of walking, going up stairs by advancing one step higher on each step with left and right legs alternatively, and standing) by actively controlling rotation angle of the knee joint using drive force of thedrive section1.
• Also, with the technology described in the previously mentioned non-patent publication by Elliott J. Rouse, Luke M. Mooney and Hugh M. Herr, “Clutchable series-elastic actuator: Implications for prosthetic knee design,” Oct. 9, 2014, doi: 10.1177/0278364914545673, The International Journal of Robotics Research, November 2014 vol. 33 no. 13 1611-1625, there were the following problems.
• • a structure for converting linear motion of an elastic mechanism to rotational motion of a knee is extremely complex, and has many components. Accordingly, it becomes heavy;
  • if movable angle of the knee joint is widened, a pulley is made large in size;
  • in order to prevent interference between component parts (elastic elements) and the knee, it is necessary to arrange a pulley at a side surface of the prosthetic leg. If this is done, then in order to maintain balance a need arises to use two pulley mechanisms in a single prosthetic leg (a single pulley mechanism comprises two pulleys, a single connecting cable, and related components).
  • pulley cables have a problem with regard to durability, and it's easy for maintenance costs to become high.
• By contrast, according to the knee joint of this embodiment that has been described, it is possible to demonstrate the following advantages:
• • since a crank mechanism is used, it is possible to restrict size increase of the knee joint overall even when moveable angle of the knee joint is widened;
  • since it is possible to use a single crank mechanism that is small and lightweight instead of the pulley mechanism, it is possible to provide a small and lightweight prosthetic leg;
  • a crank mechanism generally has high durability compared to a pulley, and so it is possible to keep maintenance costs low.
• (Fitting of the Knee Joint)
• Next, an example of the knee joint of this embodiment having been fitted to a user will be described with reference toFIG.21. With this example, a lower end of thesocket200 is connected to theupper connection section4 of the knee joint100, and thefoot section300 is connected to thelower connection section6 of theknee joint100. With the illustrated example, the prosthetic leg is made up of the knee joint100, thesocket200, and thefoot section300. It should be noted that for the connection of theupper connection section4 and thesocket200, and the connection of thelower connection section6 and thefoot section300, it is possible to use a similar attachment (not illustrated) to that in the conventional art.
• (Walking Operation Using Prosthetic Leg)
• Next, a walking operation using the prosthetic leg of this embodiment will be described further referencingFIG.22. It should be noted that in this drawing reference numeral L has been attached to the prosthetic leg.
• (FIG.22 (a) to (b))
• If the foot section of the prosthetic leg lands on the floor, then with the knee joint of this embodiment, a pressing force is applied downwards on thelinear motion member23 from thesocket200 via thecrank mechanism3, and as a result thefirst spring221 of theelastic member22 is elastically deformed and that energy is stored. However, since thelinear motion member23 is attached to theball screw13 via the drivenmember21, it is possible to produce a resistance force against movement of the drivenmember21 by causing the motor to act in a direction opposite to the direction in which the ball screw rotates, and it is possible to conserve the energy of theelastic member22.
• Here, with this embodiment, by appropriately setting spring force and initial position of theelastic member22, it is possible to set bending angle (bending angle due to passive deformation) of the knee joint for the time points where the foot section is grounded (FIGS.22 (a) and (b)) to about 20°. If this is done, there are the advantages in which it is possible to realize a knee bending angle of about 20° for the purpose of impact absorption at the time of grounding that is innate to people, and it is possible to improve usage sensitivity for the user.
• Also, with this embodiment, a repulsive force from the floor that has acted on the foot section is transmitted to the user by way of theelastic member22, which means that it is possible to absorb impact at the time of grounding, and it is possible to reduce advancement of fatigue on the user.
• (FIG.22 (b) to (d))
• Continuing on, during a walking operation, the energy that was stored in theelastic member22 is released. As a result, thelinear motion member23 is caused to move and it is possible to extend the knee joint.
• (FIG.22 (d) to (e))
• After that, with this embodiment, themotor11 is made to operate to bend the knee joint (refer, for example, toFIG.12). In this way, it is possible to store energy in theelastic member22.
• (FIG.22 (e) to (f))
• If walking advances further, with this embodiment themotor11 is driven in a reverse direction, and the knee joint is extended. Here, with this embodiment, energy that has been stored in theelastic member22 supplements the extension operation of the knee joint and so it is possible to reduce the drive force required in themotor11. Accordingly, with this embodiment battery size reduction and long battery life can be expected.
• Also, in a case where friction resistance between theball screw13 and thelinear motion member23 has been set low, there is the advantage in which it is possible to perform power regeneration with themotor11, utilizing elastic force of the previously describedelastic member22.
• Next, operation of thecrank mechanism3 of this embodiment will be described in detail with further reference toFIG.23 toFIG.28.
• First of all, for the purposes of operational description, the structure of the knee joint of the previously described embodiment is schematically shown inFIG.23. In this diagram, themotor11, transmission (speed change mechanism)12, and spring (elastic member)22 are shown as a single actuator. The mechanism ofFIG.23 is further shown schematically inFIG.24.
• A reduction ratio of the knee joint that uses this crankmechanism3 is expressed by the following equation.
• $K\frac{2\pi N_{b}R}{L_b{N}_m}$
• Here,
• • N_mis the number of teeth of amotor11 side pulley of thespeed change mechanism12;
  • N_bis the number of teeth of aball screw13 side pulley of thespeed change mechanism12;
  • L_bis the lead of theball screw13;
  • R is the radius of gyration of thearm member32; and
  • K is the reduction coefficient due to crank mechanism.
• Here, since each variable other than K is considered to be a constant in this description, detailed description will be omitted. The reduction coefficient K of the crank mechanism is expressed as follows.
• $K=\frac{\mathrm{Sin}\left(\alpha -\beta \right)}{\mathrm{Cos}\beta }$
• Here,
• • α is the angle ofarm member32 with respect to the vertical direction (vertical direction inFIG.24);
  • β is the angle of connectingrod31 with respect to vertical direction (vertical direction inFIG.24).
• Due to the influence of reduction coefficient K, the reduction ratio of the crank mechanism becomes as shown inFIG.25. With this characteristic, the reduction ratio changes in accordance with change in knee angle, and the reduction ratio becomes maximum around knee angle α=80° Specifically, with the crank mechanism of this embodiment, it is possible to move the knee joint at a different reduction ratio in accordance with change in the knee angle.
• One example of change over time of knee angle in accordance with a person walking is shown inFIG.26. As shown in this drawing, during walking, the knee angle changes between about 0° and 80°. Also, for example, when going up and down stairs or standing up from a chair, there is instantaneously a large change from a knee angle of about 80° to a knee angle of about 0°. In a case such as this, where a large angle change is necessary from a deep knee angle, then in order to cause rotation of the knee joint, a large torque becomes necessary. With this embodiment, for a deep knee angle of about 80°, it is possible to obtain a high reduction ratio. If this is done, there is the advantage in which it is possible to provide a large torque to the knee joint without imposing a large load on themotor11.
• Also, in the case of a quick pace, with a knee joint, while a fast rotation speed is required with a shallow knee angle, high torque is not required. With the crank mechanism of this embodiment, in the case of a shallow knee angle (for example, 0° to 20°), since there is a low reduction ratio there is the advantage in which increasing rotation speed of the knee joint becomes easy.
• Conversely, in the case where a pulley mechanism (refer to the previously described non-patent publication by Elliott J. Rouse, Luke M. Mooney and Hugh M. Herr, “Clutchable series-elastic actuator: Implications for prosthetic knee design,” Oct. 9, 2014, doi: 10.1177/0278364914545673, The International Journal of Robotics Research, November 2014 vol. 33 no. 13 1611-1625) is used instead of the crank mechanism, then since a reduction coefficient K does not exist in the pulley mechanism, the reduction ratio with the pulley mechanism becomes constant regardless of the knee angle. Accordingly, in the event that large torque is necessary, a large load is liable to arise in the motor. Also, in the case where a speed change mechanism is not used (refer to the previously described International patent application 2004/017872), a similar problem arises. Contrasting with this, with the knee joint of this embodiment, by using the crank mechanism there is the advantage in which it is possible to reconcile high torque and high rotation speed.
• An example where offset amount between center of rotation of thecrank mechanism3 and the serieselastic mechanism2 has been changed is shown inFIG.27. A characteristic of reduction ratio after change in offset amount is shown by the solid line inFIG.28. The dot and dash line inFIG.28 is a characteristic of the example ofFIG.25. As will be understood from this drawing, by changing the offset amount, it is possible to adjust a relationship between knee angle α and reduction ratio. Accordingly, according to this embodiment, there is the advantage in which it becomes possible to obtain maximum torque with the required knee angle, by adjusting the offset amount.
• It should be noted that the content of the present disclosure is not limited by the previously described embodiments. The present disclosure may additionally be subject to various changes to the basic structure, within a range disclosed in the scope of the patent claims.
DESCRIPTION OF THE NUMERALS
• • 1 drive section
  • 11 motor
  • 12 speed change mechanism
  • 13 ball screw
  • 2 series elastic mechanism
  • 21 driven member
  • 22 elastic member
  • 221 first spring
  • 222 second spring
  • 23 linear motion member
  • 231 first contact section
  • 232 second contact section
  • 233 linear motion rod
  • 24 guide shaft
  • 3 crank mechanism
  • 31 connecting rod
  • 32 arm member
  • 33 rotation shaft
  • 4 upper connection section
  • 5 frame
  • 51 cover
  • 52 upper base
  • 53 lower base
  • 6 lower connection section
  • 100 knee joint
  • 200 socket
  • 300 foot section
  • L prosthetic leg
• The various embodiments described above can be combined to provide further embodiments. All of the patent publications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various publications to provide yet further embodiments.
• These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.

Claims (6)

1. A knee joint, comprising a motor, a linear motion member that reciprocates in a linear direction in accordance with rotation of a ball screw that is rotated by the motor, and a crank mechanism for changing a knee angle, wherein:

the crank mechanism comprises a connecting rod that is rotatably connected to the linear motion member, an arm member that is attached to the connected rod so as to be capable of rotating and that swings in accordance with movement of the connecting rod, and a rotation shaft constituting a center of rotation when the arm member swings, and the crank mechanism converts linear motion of the linear motion member to rotational motion; and

a reduction ratio of the crank mechanism becomes a maximum value when the knee angle is about 80° to 90°, and is a lower reduction ratio than the maximum value when the knee angle is about 0° to 20°, and is set so that reduction ratio becomes lower as knee angle becomes smaller.

2. The knee joint ofclaim 1, wherein a point of connection between the linear motion member and the connecting rod is arranged offset by a specified offset amount from a rotational center of the rotation shaft, and

the specified offset amount is determined so that the reduction ratio becomes a maximum value when the knee angle is about 80° to 90°.

3. The knee joint ofclaim 1, further comprising an upper connection section for connecting a socket and the knee joint, wherein:

the crank mechanism is connected to the upper connection section, and is configured to cause rotational movement of the upper connection section in forward and backward directions.

4. The knee joint ofclaim 1, wherein the linear motion member includes a linear motion rod that extends in a movement direction of the linear motion member, and

the connecting rod is rotatably connected to an end part of the linear motion rod.

5. The knee joint ofclaim 1, further comprising a frame, wherein a rotational shaft of the crank mechanism is supported by the frame.

6. A prosthetic leg provided with the knee joint ofclaim 1.

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