Patent Description:
Prostheses (prosthetic arms, prosthetic legs) have been known as joint devices including two members that are relatively movably linked with each other. For example, a prosthetic leg (transfemoral prosthesis) attachable to a femoral region of a lower extremity amputated at a position proximal to the knee joint is a type of knee joint device that includes an above-knee member and a below-knee member linked with each other such that the members can rotationally move relative to each other around a linking unit corresponding to the knee.

Such a prosthetic leg has a yielding function of bending, at a moderate degree of hydraulic resistance, around the linking unit corresponding to the knee joint. This function can prevent the knee part of the prosthetic leg from abruptly bending upon application of a load. This function also enables a wearer to descend a staircase by swinging the prosthetic leg and his/her ordinary leg forward in turn.

A known prosthetic leg is configured such that based on detected information from a sensor that detects contractile motion of muscles and is provided at a socket where a stump is received, a degree of throttling of a variable valve of a hydraulic cylinder is controlled, so that resistance to bending and straightening a knee joint is adjusted (see, for example, <CIT>).

<CIT> shows a joint device according to the preamble of claim <NUM>.

However, while being capable of bending the knee part by the yielding function, the conventional prosthetic leg cannot straighten the knee part without being swung forward. That is, with the conventional prosthetic leg, the wearer cannot straighten the knee part while bracing the prosthetic leg with application of a load to the prosthetic leg and while moving his/her body upward. Therefore, the conventional prosthetic leg does not allow the wearer to ascend a staircase with a nearly normal gait.

In view of the foregoing background, it is an object of the present invention to provide a joint device that can be straightened from a bent state, while a load is applied to the joint device.

The invention provides a joint device according to claim <NUM>.

According to the features of claim <NUM>, the joint device can be straightened from a state where the first and second members form a bend, while a load is applied to the joint device.

Further, by the connection and disconnection unit the rotational power of the rotary unit can be interrupted to be prevented from being transmitted to the conversion unit, thereby inhibiting application of an unnecessary load to the rotary unit.

Further, when an external force acting in a direction in which the rotary unit and the conversion unit are arranged becomes less intense than the urging force of the first urging part, by the first urging part, the connection and disconnection unit can be automatically brought into a disconnected state.

According to the features of claim <NUM>, the rotational power of the rotary unit can be generated by means of the rotational power of the rotating machine.

According to the features of claim <NUM>, the rotational power of the rotating machine can be suitably controlled by the control unit.

According to the features of claim <NUM>, while waste of power consumption and heat generation by the rotating machine is reduced, the rotating machine can be controlled to generate the rotational power in the direction, which is converted by the conversion unit into the translational motion in the extension direction.

According to the features of claim <NUM>, since the rotary unit is heavier than the conversion unit composed of an outer cylinder and a spindle, when the wearer walks in a normal manner by swinging the prosthetic leg and his/her ordinary leg forward in turn, inertia caused by the weight of the rotary unit can be effectively used. Further since a center of gravity of the prosthetic leg is at a low position, the posture of the wearer is stabilized when he/she is in a standing position.

By the features of claim <NUM>, it is possible to increase a degree of freedom in selection of a drive power generator of the rotary unit.

By the features of claim <NUM>, it is possible to adjust a relative rotational movement of the first and second members, thereby making it less likely for an abrupt bend to occur between the first and second members.

The features of claim <NUM> make it possible to estimate a state of the joint device, based on the external force acting in the contraction direction and applied to the extension and contraction device.

The features of claim <NUM> make it possible to estimate a state of the joint device from the acceleration of the first member.

The features of claim <NUM> make it possible to estimate a state of the joint device from the angle formed by the first member and the second member.

The features of claim <NUM> make it possible for the rotary unit in the joint device to generate the rotational power, without external supply of electric power.

The features of claim <NUM> provide the joint device attachable to the lower extremity of the wearer's body.

The features of claim <NUM> provide the knee joint device attachable to the lower extremity of the wearer's body.

The present invention provides a joint device that can be straightened from a bent state, while a load is applied to the joint device.

An embodiment of a joint device according to the present invention will be described in detail with reference to the drawings. The present specification describes, as an example of the joint device, a transfemoral prosthesis (hereinafter referred to as the prosthetic leg) that is a type of knee joint device attachable to a part to serve as a knee joint and located in a femoral region of a lower extremity.

<FIG> is a side view illustrating principal components of the prosthetic leg in cross section. As illustrated in <FIG>, the prosthetic leg <NUM> has a below-knee member <NUM> and an above-knee member <NUM>. The below-knee member <NUM> is coupled to the above-knee member <NUM> via a knee joint mechanism <NUM>. The below-knee member <NUM> corresponds to a "first member" of the present invention. The above-knee member <NUM> corresponds to a "second member" of the present invention. The below-knee member <NUM> has a lower end coupled to a foot part <NUM>. The above-knee member <NUM> is disposed at an upper end of the below-knee member <NUM>. The above-knee member <NUM> has an upper end coupled to a socket <NUM> that is configured to receive a stump of a femoral region of a lower extremity of a wearer's body (human body; not illustrated).

Note that directions with respect to the prosthetic leg <NUM> will be described based on a state in which the wearer's body having the prosthetic leg <NUM> attached thereto is in a standing position. Specifically, "above/upper/upward" and "below/lower/downward" with respect to the prosthetic leg <NUM> correspond to "above/upper/upward" and "below/lower/downward" with respect to the wearer's body in the standing position, and correspond to upward and downward directions in <FIG>. "Front/forward" and "rear/rearward" (a front face and a rear face) with respect to the prosthetic leg <NUM> correspond to "front/forward" and "rear/rearward" (a front face and a rear face) with respect to the wearer's body in the standing position, and correspond to right and left directions in <FIG>.

The knee joint mechanism <NUM> corresponds to the knee of the prosthetic leg <NUM>, and links the below-knee member <NUM> with the above-knee member <NUM> such that the below-knee member <NUM> and the above-knee member <NUM> can rotationally move relative to each other around a centered pivot shaft <NUM> in the forward and rearward directions of the prosthetic leg <NUM> (in clockwise and counterclockwise directions in <FIG>). The knee joint mechanism <NUM> corresponds to a "linking unit" of the present invention.

In the following, the relative rotational movement of the below-knee member <NUM> and the above-knee member <NUM> around the pivot shaft <NUM> of the knee joint mechanism <NUM> will be described based on a case where the below-knee member <NUM> is stationary while the above-knee member <NUM> rotationally moves in the forward direction (clockwise direction) or the rearward direction (counterclockwise direction) in <FIG>.

The knee joint mechanism <NUM> of the present embodiment includes a rotary damper <NUM> configured to adjust the rotational movement of the knee joint mechanism <NUM>. The rotary damper <NUM> is rotatable around the pivot shaft <NUM> of the knee joint mechanism <NUM>, and adjusts the relative rotational movement of the below-knee member <NUM> and the above-knee member <NUM> around the pivot shaft <NUM>, into a movement at a moderate degree of hydraulic resistance. The prosthetic leg <NUM> of the present embodiment includes the rotary damper <NUM> provided to the knee joint mechanism <NUM>, and thereby performs a function of preventing abrupt knee bending and a yielding function. The rotary damper <NUM> corresponds to an "adjustment unit" of the present invention.

The above-knee member <NUM> is mounted such that it can rotationally move around the pivot shaft <NUM> of the knee joint mechanism <NUM>, in the forward and rearward directions of the prosthetic leg <NUM>. The above-knee member <NUM> has a socket-coupling projection <NUM> having an upper end couplable to the socket <NUM>, and an arm part <NUM> extending from a portion directly under the socket-coupling projection <NUM> in the rearward direction with respect to the prosthetic leg <NUM>, specifically, in the rearward direction with respect to the knee joint mechanism <NUM>.

The below-knee member <NUM> corresponds to the crus of the prosthetic leg <NUM>, and forms a main portion of the prosthetic leg <NUM>. The below-knee member <NUM> of the present embodiment has, in a frame <NUM> corresponding to the lower leg of the prosthetic leg <NUM>, an extension/contraction device <NUM>, a battery <NUM>, a six-axis force sensor <NUM>, and a six-axis motion sensor <NUM>, a knee joint angle sensor <NUM>, and a control unit <NUM>. The knee joint mechanism <NUM> is disposed in an upper end portion of the frame <NUM>. Note that wires electrically connecting the components to each other are omitted from <FIG>.

The extension/contraction device <NUM> is disposed in a rear portion of an interior of the frame <NUM> and is extendible and contractable in the upward/downward direction. The extension/contraction device <NUM> has a lower end attached to a first pivot 18a disposed in proximity to a lower end of the interior of the frame <NUM> by means of an attachment part 12a such that the lower end of the extension/contraction device <NUM> is pivotable in the forward/rearward direction of the prosthetic leg <NUM>. On the other hand, the extension/contraction device <NUM> has an upper end exposed to the outside from the frame <NUM> and attached to a second pivot 18b disposed at a leading end of the arm part <NUM> of the above-knee member <NUM> by means of an attachment part 12b such that the upper end of the extension/contraction device <NUM> is pivotable in the forward/rearward direction of the prosthetic leg <NUM>. Thus, the extension/contraction device <NUM> is disposed between the below-knee member <NUM> and the above-knee member <NUM>. When the extension/contraction device <NUM> extends or contracts, the arm part <NUM> of the above-knee member <NUM> moves upward or downward, thereby causing the above-knee member <NUM> to pivot around the pivot shaft <NUM> of the knee joint mechanism <NUM>. In this way, an angle formed by the below-knee member <NUM> and the above-knee member <NUM> is varied.

The extension/contraction device <NUM> of the present embodiment has a rotary unit <NUM> that generates a rotational power, and a conversion unit <NUM> that converts the rotational power generated by the rotary unit <NUM> into translational motion in an extension/contraction direction. A clutch unit <NUM> capable of connecting and disconnecting power transmission from the rotary unit <NUM> to the conversion unit <NUM> is further provided between the rotary unit <NUM> and the conversion unit <NUM>.

The rotary unit <NUM> has a rotating machine <NUM> functioning as a drive power generator. The rotating machine <NUM> is housed in a cylindrical housing <NUM> having an open top end, and generates the rotational power upon supply of electric power from the battery <NUM>. The housing <NUM> is pivotably attached to the first pivot 18a disposed in the lower end portion of the interior of the frame <NUM> by means of the attachment part 12a. The housing <NUM> is disposed rearwardly obliquely from the first pivot 18a. Specific examples of the rotating machine <NUM> are not particularly limited, but may include a stepping motor, a DC motor, etc. The rotating machine <NUM> is housed in a lowermost portion of an interior of the housing <NUM>, while having an output shaft (not illustrated) facing upward.

The rotary unit <NUM> of the present embodiment further has a transmission <NUM> that is housed in the housing <NUM>, together with the rotating machine <NUM>. The transmission <NUM> is coupled to the output shaft of the rotating machine <NUM>, and outputs the rotational power while varying a ratio of a rotational speed of the output shaft. This configuration makes it possible to increase a degree of freedom in selection of the rotating machine <NUM> to be used in the rotary unit <NUM>. As the transmission <NUM>, a speed reducing gear or a speed increasing gear can be used. In the case of using the speed reducing gear, the rotational power of the rotating machine <NUM> can be converted into a rotational power with a high torque. On the other hand, in the case of using the speed increasing gear, the rotational power of the rotating machine <NUM> can be converted into a high-speed rotational power.

The conversion unit <NUM> has an outer cylinder <NUM> having an open bottom end, and a spindle <NUM> extending from the outer cylinder <NUM> to the housing <NUM> and having a rod shape.

The outer cylinder <NUM> is pivotably attached to the second pivot 18b disposed on the arm part <NUM> of the above-knee member <NUM> by means of the attachment part 12b, and extends from the second pivot 18b toward the housing <NUM> so as to be inserted in the frame <NUM>. The outer cylinder <NUM> has, on an inner peripheral surface thereof, a female thread 126a helically extending along substantially the entire axial length of the outer cylinder <NUM>.

The spindle <NUM> has, on an outer peripheral surface thereof, a male thread 127a extending along substantially the entire axial length of the spindle <NUM>, and engageable with the female thread 126a in the outer cylinder <NUM>. The spindle <NUM> has an upper end portion engaged with the female thread 126a in the outer cylinder <NUM>, whereby the upper end portion of the spindle <NUM> can rotate around an axis thereof, while being received in the outer cylinder <NUM>. On the other hand, the spindle <NUM> has a lower end portion attached to an upper end of the interior of the housing <NUM> such that the lower end portion is rotatable around its axis, but is allowed to move only by a distance within a range of a connection/disconnection movement of the clutch unit <NUM>, which will be described later. In the housing <NUM>, the spindle <NUM> is arranged to be able to transmit the rotational power of the rotating machine <NUM>. The spindle <NUM> corresponds to a "rotary body" of the present invention.

The spindle <NUM> rotates around its axis when the rotational power of the rotating machine <NUM> in the housing <NUM> is transmitted to the spindle <NUM>. Rotation of the spindle <NUM> moves the outer cylinder <NUM>, which is threaded on the spindle <NUM>, upward or downward in the axial direction of the spindle <NUM>. As a result, a distance by which the outer cylinder <NUM> is spaced apart from the housing <NUM> varies, and the entire length of the extension/contraction device <NUM> increases or decreases. Specifically, the spindle <NUM> and the outer cylinder <NUM> forming the conversion unit <NUM> are configured to convert the rotational power generated by the rotary unit <NUM> into translational motion in the extension/contraction direction. When extending or contracting, the extension/contraction device <NUM> moves the arm part <NUM>, to which the outer cylinder <NUM> is attached by means of the second pivot 18b, upward or downward, and causes the above-knee member <NUM> to pivot around the pivot shaft <NUM> in the forward or rearward direction of the prosthetic leg <NUM>, thereby varying the angle formed by the below-knee member <NUM> and the above-knee member <NUM>.

The extension/contraction device <NUM> of the present embodiment is configured to move the outer cylinder <NUM> in an extension direction when the rotational power from the rotary unit <NUM> rotates the spindle <NUM> around its axis in a direction (forward rotation) on one hand, and is configured to move, in a contraction direction, the outer cylinder <NUM> that has been moved in the extension direction when the rotational power from the rotary unit <NUM> rotates the spindle <NUM> around its axis in a direction opposite to the above direction (backward rotation) on the other hand. A configuration causing the spindle <NUM> to rotate backward around its axis will be described later.

In the frame <NUM>, the conversion unit <NUM> and the rotary unit <NUM> of the extension/contraction device <NUM> of the present embodiment are arranged such that the rotary unit <NUM> is more distant from the above-knee member <NUM> (and closer to the foot part <NUM> of the prosthetic leg <NUM>) than the conversion unit <NUM> is. In other words, the outer cylinder <NUM> and the housing <NUM> including the rotary unit <NUM> are arranged in an upper portion and a lower portion of the prosthetic leg <NUM>, respectively, while having the spindle <NUM> interposed therebetween. Since the rotary unit <NUM> is heavier than the conversion unit <NUM> composed of the outer cylinder <NUM> and the spindle <NUM>, when a wearer of the prosthetic leg <NUM> walks in a normal manner by swinging the prosthetic leg <NUM> and his/her ordinary leg forward in turn, inertia caused by the weight of the rotary unit <NUM> can be effectively used. Further since a center of gravity of the prosthetic leg <NUM> is at a low position, the posture of the wearer is stabilized when he/she is in the standing position.

The clutch unit <NUM> has a first engagement element 123a coupled to a side of the rotary unit <NUM>, and a second engagement element 123b coupled to a side of the conversion unit <NUM>, and is disposed in the housing <NUM> of the extension/contraction device <NUM> such that clutch unit <NUM> can connect and disconnect the power transmission from the rotary unit <NUM> to the conversion unit <NUM>. The clutch unit <NUM> corresponds to a "connection/disconnection unit" of the present invention. The first engagement element 123a corresponds to a "first connection/disconnection member" of the present invention. The second engagement element 123b corresponds to a "second connection/disconnection member" of the present invention.

<FIG> is an enlarged diagram schematically illustrating an embodiment of the clutch unit <NUM> provided to the extension/contraction device <NUM>. The first engagement element 123a is provided on an output shaft 125a of the transmission <NUM> forming part of the rotary unit <NUM>, and projects upward toward the spindle <NUM>. On the other hand, the second engagement element 123b is provided on a lower end portion 127b of the spindle <NUM>, and projects downward toward the transmission <NUM>. The first engagement element 123a has a surface facing a surface of the second engagement element 123b. The surface of the first engagement element 123a and the surface of the second engagement element 123b have pawls 123c and pawls 123d, respectively, which can be meshed with each other.

The pawls 123c of the first engagement element 123a and the pawls 123d of the second engagement element 123b may have any specific shape, as long as the rotational power of the rotary unit <NUM> can be transmitted to the spindle <NUM> when the pawls 123c and 123d are meshed with each other. The pawls 123c and 123d may have a trapezoidal shape in cross section as illustrated in <FIG>, or a rectangular shape in cross section as illustrated in <FIG>. Alternatively, the pawls 123c and 123d may have a sawtooth shape in cross section as illustrated in <FIG>.

The transmission <NUM> has an output-side end surface 125b and the spindle <NUM> has a lower end surface 127c. A spring <NUM> is disposed between the end surfaces 125b and 127c. The spring <NUM> is constituted by an appropriate elastic member, such as a coil spring, and accommodates therein the first engagement element 123a and the second engagement element 123b. The spring <NUM> is configured to constantly apply an urging force to the output-side end surface 125b of the transmission <NUM> and the spindle <NUM> in a direction in which the first engagement element 123a and the second engagement element 123b are spaced apart from each other and the pawls 123c and 123d are unmeshed from each other. The spring <NUM> is also configured to contract in the axial direction when an axial load having a predetermined intensity acts on the spindle <NUM> such that the pawls 123c of the first engagement element 123a and the pawls 123d of the second engagement element 123b can be meshed with each other. When the spring <NUM> deforms to cause the first engagement element 123a to mesh with the second engagement element 123b, the rotational power generated by the rotary unit <NUM> is transmitted via the transmission <NUM> to the spindle <NUM>. The spring <NUM> corresponds to a "first urging part" of the present invention.

The urging force of the spring <NUM> of the present embodiment is set such that when the above-knee member <NUM> is caused to pivot rearward (in the counterclockwise direction) around the pivot shaft <NUM> and an axial load is applied to the extension/contraction device <NUM>, the spring <NUM> contracts in the axial direction, thereby causing the first engagement element 123a and the second engagement element 123b to mesh with each other.

As illustrated in <FIG>, the spring <NUM> of the present embodiment is constituted by a coil spring. In this case, the spring <NUM> may have one end fixed to the output-side end surface 125b of the transmission <NUM>, and the other end fixed to the lower end surface 127c of the spindle <NUM>. This configuration allows the spring <NUM> to function also as an urging member configured to urge the spindle <NUM> in one rotation direction. Specifically, when the spring <NUM> contracts in the axial direction to cause the first engagement element 123a to mesh with the second engagement element 123b, the rotational power of the rotary unit <NUM> is transmitted via the clutch unit <NUM> to the spindle <NUM>, so that the spindle <NUM> rotates in the forward direction while twisting the spring <NUM> against the urging force acting in the rotation direction. When the application of the load to the extension/contraction device <NUM> is stopped, the spring <NUM> elastically resumes its original shape in the axial direction, so that the first engagement element 123a becomes unmeshed from the second engagement element 123b and the clutch unit <NUM> is brought into a disconnected state. In this way, the spring <NUM> elastically resumes, by the urging force, its original shape from the twisted state around the axis, and rotates the spindle <NUM> backward. Thus, the spring <NUM> having the above configuration corresponds to a "second urging part" of the present invention.

The battery <NUM> is constituted by, for example, a lithium-ion secondary battery capable of charging and discharging, and is disposed forward of the extension/contraction device <NUM> in the frame <NUM>. The battery <NUM> is connected to be able to supply the rotating machine <NUM> of the rotary unit <NUM> with electric power, and to be able to supply the six-axis force sensor <NUM>, the six-axis motion sensor <NUM>, the knee joint angle sensor <NUM>, and the control unit <NUM> with electric power required for driving the respective components. In general, the battery <NUM> is detachably incorporated in the frame <NUM>. However, the battery <NUM> may be chargeable by way of contact or non-contact (wired or wireless) charging from an external device, while remaining in the frame <NUM>.

When a rotary force from the spindle <NUM> acts on the rotating machine <NUM> when it is not in operation, the rotating machine <NUM> functions as a generator to convert the rotary force into electric power. The battery <NUM> of the present embodiment may be configured to be able to regenerate the electric power provided through the conversion by the rotating machine <NUM>.

The six-axis force sensor <NUM> is capable of detecting three-axis load and three-axis moment of the prosthetic leg <NUM> in the forward/rearward direction, the right/left direction, and the upward/downward direction, and is disposed in a lower end portion of the interior of the frame <NUM>. The six-axis force sensor <NUM> acquires information regarding an external force acting in a contraction direction and applied to the extension/contraction device <NUM>, based on a detection signal that is detected when the foot part <NUM> of the prosthetic leg <NUM> attached to a wearer's body contacts with the ground or the like. The detection result is transmitted to the control unit <NUM>. The six-axis force sensor <NUM> corresponds to a "first acquisition unit" of the present invention.

The six-axis motion sensor <NUM> is capable of detecting three-axis acceleration and three-axis angular acceleration of the prosthetic leg <NUM> in the forward/rearward direction, the right/left direction, and the upward/downward direction, and is disposed directly under the knee joint mechanism <NUM>, in an upper portion of the interior of the frame <NUM>. The six-axis motion sensor <NUM> acquires information regarding an acceleration acting on the prosthetic leg <NUM>, based on a detection signal that is detected when the prosthetic leg <NUM> attached to the wearer's body moves. The detection result is transmitted to the control unit <NUM>. The six-axis motion sensor <NUM> corresponds to a "second acquisition unit" of the present invention.

The knee joint angle sensor <NUM> is a sensor capable of detecting angle information, such as a rotary encoder, and is provided at the knee joint mechanism <NUM>. The knee joint angle sensor <NUM> acquires information regarding the angle that is formed by the below-knee member <NUM> and the above-knee member <NUM>, as a consequence of a relative rotational movement of the members. The detection result is transmitted to the control unit <NUM>. The knee joint angle sensor <NUM> corresponds to a "third acquisition unit" of the present invention.

The control unit <NUM> is constituted by, for example, an electronic control unit (ECU), and is configured to control the rotational power of the rotating machine <NUM>. Specifically, the control unit <NUM> estimates a state of the prosthetic leg <NUM> based on the detection results transmitted from the six-axis force sensor <NUM>, the six-axis motion sensor <NUM>, and the knee joint angle sensor <NUM>, and outputs a control signal to the rotating machine <NUM> to cause the rotating machine <NUM> to generate a rotational power suitable for the state of the prosthetic leg <NUM>.

Next, movements of the prosthetic leg <NUM> will be specifically described with reference to <FIG> and <FIG>. <FIG> is a diagram illustrating the prosthetic leg in a stair-ascending state, the prosthetic leg being in contact with a step of a staircase. <FIG> is an enlarged diagram schematically illustrating the clutch unit provided to the extension/contraction device, the clutch unit being in a meshed state. <FIG> is a diagram illustrating the prosthetic leg in a state where the extension/contraction device is extended. <FIG> is a diagram schematically illustrating the wearer's body having the prosthetic leg attached thereto and ascending a staircase.

First, reference is made to <FIG> illustrating prosthetic leg <NUM> in the standing position. In this position, a femoral region of a lower extremity of the wearer's body (not illustrated) is applying a load in a substantially vertical direction to the prosthetic leg <NUM> via the socket <NUM>, in the direction from the above-knee member <NUM> to the foot part <NUM>. At this time, the above-knee member <NUM> is not caused to pivot rearwardly, and an external force (body weight) in the contraction direction does not act on the extension/contraction device <NUM>. Therefore, the spring <NUM> exerts an urging force to space the spindle <NUM> and the rotary unit <NUM> of the extension/contraction device <NUM> apart from each other, whereby the first engagement element 123a and the second engagement element 123b of the clutch unit <NUM> is spaced apart from each other. Accordingly, even when the rotating machine <NUM> is driven and rotated, the rotational power of the rotating machine <NUM> is not allowed to act on the spindle <NUM>, and the extension/contraction device <NUM> is prevented from operating. Since the rotating machine <NUM> does not receive any load, the rotating machine <NUM> is inhibited from generating heat.

At this time, the control unit <NUM> estimates that the prosthetic leg <NUM> is in the standing position, based on the detection results transmitted from the six-axis force sensor <NUM>, the six-axis motion sensor <NUM>, and the knee joint angle sensor <NUM>, and performs control such that the rotating machine <NUM> stops or is inhibited from generating an unnecessary rotational power. This configuration reduces waste of power consumption.

When the prosthetic leg <NUM> transitions to flat-ground walking (a walking mode) and a load is applied to a heel area of the prosthetic leg <NUM> in a stance phase, the above-knee member <NUM> is caused to pivot rearward (in the counterclockwise direction) around the pivot shaft <NUM> of the knee joint mechanism <NUM>. The pivotal movement of the above-knee member <NUM> moves the arm part <NUM> downward, and accordingly, an external force acting in the contraction direction is applied to the outer cylinder <NUM> of the extension/contraction device <NUM>. Consequently, the outer cylinder <NUM> presses the spindle <NUM> in the axial direction toward the rotary unit <NUM>, thereby causing the spring <NUM> disposed between the transmission <NUM> of the rotary unit <NUM> and the spindle <NUM> to contract in the axial direction, so that the first engagement element 123a and the second engagement element 123b of the clutch unit <NUM> are meshed with each other. Concurrently with this, the rotary damper <NUM> of the knee joint mechanism <NUM> adjusts the pivotal movement of the above-knee member <NUM> into a movement at a moderate degree of hydraulic resistance, thereby preventing abrupt knee bending. The external force acting in the contraction direction and applied at this time to the extension/contraction device <NUM> is a force (load) greater than a rotational torque of the rotating machine <NUM>. Therefore, the rotary unit <NUM> cannot rotate the spindle <NUM> in the forward direction, so that the extension/contraction device <NUM> does not extend.

In the walking mode, for example, when the prosthetic leg <NUM> transitions from the stance phase to a swing phase and the application of the external force acting in the contraction direction to the extension/contraction device <NUM> is stopped, the spring <NUM> elastically resumes its original shape in the axial direction to cause the spindle <NUM> to move the outer cylinder <NUM> upward to its original position, so that the above-knee member <NUM> is caused to pivot forward (in the clockwise direction) around the pivot shaft <NUM>. As a result, the prosthetic leg <NUM> returns to the standing position and becomes ready for next application of a load.

Next, a case where the wearer with the prosthetic leg <NUM> ascends a staircase S will be described. As illustrated in <FIG>, when the wearer moves his/her femoral region upward, the prosthetic leg <NUM> is raised above his/her normal foot and then contacts with an upper step of the staircase S. At this time, the above-knee member <NUM> is caused to pivot rearward (in the counterclockwise direction) around the pivot shaft <NUM> of the knee joint mechanism <NUM>, thereby moving the leading end of the arm part <NUM> downward. That is, the prosthetic leg <NUM> is brought into a state where the knee is bent. When the downward movement of the arm part <NUM> applies an external force acting in the contraction direction to the extension/contraction device <NUM>, the outer cylinder <NUM> presses the spindle <NUM> in the axial direction toward the rotary unit <NUM>, thereby causing the spring <NUM> disposed between the transmission <NUM> of the rotary unit <NUM> and the spindle <NUM> to contract in the axial direction, so that the first engagement element 123a and the second engagement element 123b of the clutch unit <NUM> are meshed with each other.

For example, an acceleration at which the prosthetic leg <NUM> is raised above a step of a staircase S and is brought into contact with the step, and a load applied to the prosthetic leg <NUM> at the time of contacting with the step are detected by the six-axis force sensor <NUM>, the six-axis motion sensor <NUM>, and the knee joint angle sensor <NUM>, whereby the control unit <NUM> estimates that the prosthetic leg <NUM> has been transitioned to a stair-ascending movement for ascending the staircase S (a stair-ascending mode). Accordingly, the control unit <NUM> outputs a signal to cause the rotating machine <NUM> to generate a rotational power required for ascending the staircase. Specifically, when a predetermined external force acting in the contraction direction is applied to the extension/contraction device <NUM> during the stair-ascending movement, the control unit <NUM> performs control such that the rotating machine <NUM> generates a rotational power acting in a direction, the rotational power being converted by the conversion unit <NUM>, which is composed of the outer cylinder <NUM> and the spindle <NUM>, into translational motion in an extension direction.

Following the contact of the prosthetic leg <NUM> with a step above the normal foot, when the wearer braces the prosthetic leg <NUM> via his/her femoral region for ascending the staircase, an external force acting in the contraction direction is applied to the extension/contraction device <NUM>. The external force applied at this time is less intense than that applied to the extension/contraction device <NUM> in the stance phase, and is a force (load) less intense than the rotational torque of the rotating machine <NUM>. Therefore, the rotary unit <NUM> rotates the spindle <NUM> coupled to the second engagement element 123b in the forward direction. As a result, as illustrated in <FIG>, the outer cylinder <NUM> moves axially upward, whereby the extension/contraction device <NUM> extends.

The extension of the extension/contraction device <NUM> causes the above-knee member <NUM> coupled to the outer cylinder <NUM> via the arm part <NUM> to pivot forward (in the clockwise direction) around the pivot shaft <NUM> of the knee joint mechanism <NUM>. Consequently, the prosthetic leg <NUM> causes the socket <NUM> coupled to the above-knee member <NUM> to move obliquely forward, and straightens the knee while raising the wearer's body as illustrated in <FIG>, thereby returns to the standing position illustrated in <FIG>. Thereafter, the above-described movements are repeated, so that he/she is allowed to ascend the staircase S using the prosthetic leg <NUM>. With the prosthetic leg <NUM> of the present embodiment, the wearer can ascend the staircase S with a nearly natural gait because the wearer can perform the stair-ascending movement by applying a load to the prosthetic leg <NUM> by bracing the prosthetic leg <NUM> in contact with an upper step, while moving upward his/her body.

In the embodiment described above, the knee joint mechanism <NUM> has the rotary damper <NUM>. However, the rotary damper <NUM> does not necessarily have to be provided. In the case of omitting the rotary damper <NUM>, when the yielding movement is performed, the control unit <NUM> controls and causes the rotating machine <NUM> to generate such a rotational power that does not extend the extension/contraction device <NUM>, so that the rotational power of the rotating machine <NUM> resists the backward rotation of the spindle <NUM> to the same or similar extent that the rotary damper <NUM> does.

Claim 1:
A joint device (<NUM>) comprising:
a linking unit (<NUM>) that links a first member (<NUM>) with a second member (<NUM>) such that the first and second members (<NUM>,<NUM>) are movable relative to each other; and
an extension and contraction device (<NUM>) that is connected between the first member (<NUM>) and the second member (<NUM>) in a manner allowing power transmission, and is capable of varying an angle formed by the first member (<NUM>) and the second member (<NUM>) around the linking unit (<NUM>) by extending and contracting,
wherein the extension and contraction device (<NUM>) includes a rotary unit (<NUM>) that is configured to generate a rotational power, and a conversion unit (<NUM>) that is connected to the rotary unit (<NUM>) in a manner allowing power transmission and is configured to convert the rotational power generated by the rotary unit (<NUM>) into translational motion in an extension and contraction direction, and includes, between the rotary unit (<NUM>) and the conversion unit (<NUM>), a connection and disconnection unit (<NUM>) that is capable of connecting and disconnecting power transmission from the rotary unit (<NUM>) to the conversion unit (<NUM>), characterized in that
the connection and disconnection unit (<NUM>) includes a first connection and disconnection member (123a) coupled to a side of the rotary unit (<NUM>) and a second connection and disconnection member (123b) coupled to a side of the conversion unit (<NUM>), and further includes a first urging part (<NUM>) that applies an urging force in a direction in which the first and second connection and disconnection members (123a, 123b) are constantly spaced apart from each other.