Walking assist device

An actuator is reduced in weight without impairing a walking assist function, and this reduces the inertial moment of a leg link. A drive crank arm on the output shaft of the actuator and a driven crank arm fixed to a second link portion so as to be concentric to the joint shaft of a third joint portion are connected to each other via a connection link. The connection link is placed so that a line connecting a pivot portion at which the drive crank arm is pivotally mounted and a pivot portion at which the driven crank arm is pivotally mounted obliquely crosses a line connecting the output shaft of the actuator and the joint shaft of the third joint portion.

PRIORITY CLAIM

The present application is based on and claims the priority benefit of Japanese Patent Application 2008-095244 filed on Apr. 1, 2008, the contents of which are incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a walking assist device for assisting a user in walking.

2. Description of the Related Art

Conventionally, as a walking assist device, there has been known one provided with a load transmit portion, a foot mounting portion mounted to a user's foot, and a leg link disposed between the load transmit portion and the foot mounting portion (for example, refer to Patent Document 1: Japanese Patent Laid-Open No. 2007-20909). The walking assist device is configured to transmit a force generated from the leg link to the user's trunk via the load transmit portion.

The leg link in the walking assist device includes an upper first link portion connected to the load transmit portion via a first joint portion, a lower second link portion connected to the foot mounting portion via a second joint portion, a middle third joint portion connected to the first link portion and the second link portion in such a way that the first link portion and the second link portion can stretch and bend freely, and a drive mechanism to drive the third joint portion.

Thereby, the load applied to a leg of the user can be alleviated according to the force generated by the drive mechanism in the direction of decreasing a flexion angle of the third joint portion (same as the direction of stretching the leg link).

In the device disclosed in Patent Document 1, the load transmit portion is composed of a seat member on which the user sits astride, and the first joint portion is composed of an arc-shaped guide rail which is connected to the seat member and is longitudinal in an anteroposterior direction with the center of curvature located above the seat member and a slider which is fixed at an upper end portion of the first link portion and is movably engaged in the guide rail.

Thereby, the center of curvature of the guide rail is equivalent to the swing fulcrum for the leg link of the first joint portion in the anteroposterior direction. Since the swing fulcrum is located above the seat member, the seat member can be prevented from inclining greatly in the vertical direction due to the shifting in the weight of the user.

Further, in the device disclosed in Patent Document 1, the slider is engaged to a part of the guide rail which is positioned at a rear side to the connection line connecting the center of curvature of the guide rail and the joint shaft of the third joint portion. Thereby, the swing stroke of the leg link to the forward so as to follow the forward movement of a free leg (the leg with foot leaving away from the floor) of the user can be assured without increasing the length of the guide rail to the forward direction too much; consequently, it is expected to reduce the size of the first joint portion.

The drive mechanism described in an embodiment of the Patent Document 1 is provided with a rotary actuator mounted to the first link portion, and a wire-typed force transmit portion configured to transmit a force from the rotary actuator to the third joint portion via a wire. However, the drive mechanism is not limited thereto, specifically, it is acceptable that the drive mechanism is provided with the rotary actuator mounted to the first link portion, a drive crank arm disposed on an output shaft of the rotary actuator, a driven crank arm fixed to at the second link portion concentrically to a joint shaft of the third joint portion, and a connection link with one end pivoted at the drive crank arm and the other end pivoted at the driven crank arm.

Generally, it has been considered to configure the drive mechanism as a parallel link mechanism by disposing the connection link in such a way that a connection line connecting a pivot portion of the connection link at which the drive crank arm is pivotally mounted and a pivot portion of the connection link at which the driven crank arm is pivotally mounted is parallel to a connection line connecting the output shaft of the rotary actuator and the joint shaft of the third joint portion.

However, if the inertial moment of the leg link around the first joint portion is greater, when the user swings the free leg to the forward, the load applied to the free leg due to the inertial moment of the leg link will become greater. Therefore, it is desired to reduce the inertial moment of the leg link. In this regarding, if the rotary actuator mounted at the first link portion is made lighter, the inertial moment of the leg link can be reduced. However, in order to generate the desired assist force for the leg link, it is necessary for the rotary actuator to output a torque of at least a certain magnitude; therefore, there is a limit on reducing the weight of the rotary actuator.

To solve this problem, it has been considered to increase the length of the driven crank arm longer than the length of the drive crank arm to decrease the rotational angular velocity of the driven crank arm slower than the rotational angular velocity of the drive crank arm so as to increase the torque transmitted to the driven crank arm, in other words, to increase the drive torque of the third joint portion greater than the output torque of the rotary actuator. However, this solution brings about the following problem, that is, for the leg link with the first link portion and the second link portion connected by the third joint portion in such a way that the first link portion and the second link portion can stretch and bend freely, the telescopic velocity of the leg link obtained by differentiating the length of the leg link (the length of a line segment connecting the first joint portion at the upper end and the second joint portion at the lower end) by the flexion angle of the third joint portion slows down as the flexion angle of the third joint portion decreases. Therefore, in order to improve the controllability in a small range of the flexion angles of the third joint portion, it is necessary to make the flexion angle vary faster. Accordingly, in the device where the rotational angular velocity of the driven crank arm is slower than the rotational angular velocity of the drive crank arm, the required rotational velocity of the rotary actuator would be greater, which makes it difficult to reduce the weight of the rotary actuator.

SUMMARY OF THE INVENTION

The present invention has been accomplished in view of the aforementioned problems, and it is therefore an object of the present invention to provide a walking assist device capable of alleviating the inertial moment of a leg link through reducing the weight of a rotary actuator without impairing a walking assist function thereof.

To attain an object described above, a walking assist device according to the present invention is provided with a load transmit portion, a foot mounting portion mounted to a user's foot, and a leg link disposed between the load transmit portion and the loot mounting portion, the walking assist device being configured to transmit a force generated from the leg link to the user's trunk via the load transmit portion, and the leg link including an upper first link portion connected to the load transmit portion via a first joint portion, a lower second link portion connected to the foot mounting portion via a second joint portion, a middle third joint portion connected to the first link portion and the second link portion in such a way that the first link portion and the second link portion can stretch and bend freely, and a drive mechanism to drive the third joint portion, wherein the drive mechanism is provided with a rotary actuator mounted to the first link portion, a drive crank arm disposed on an output shaft of the rotary actuator, a driven crank arm fixed to at the second link portion concentrically to a joint shaft of the third joint portion, and a connection link with one end pivoted at the drive crank arm and the other end pivoted at the driven crank arm, and the connection link is disposed in such a way that a connection line connecting a pivot portion of the connection link at which the drive crank arm is pivotally mounted and a pivot portion of the connection link at which the driven crank arm is pivotally mounted obliquely crosses a connection line connecting the output shaft of the rotary actuator and the joint shaft of the third joint portion.

According to the present invention, since the connection line connecting the pivot portion of the connection link at which the drive crank arm is pivotally mounted and the pivot portion of the connection link at which the driven crank arm is pivotally mounted obliquely crosses the connection line connecting the output shaft of the rotary actuator and the joint shaft of the third joint portion, the ratio between the rotational angular velocity of the driven crank arm and the rotational angular velocity of the drive crank arm varies according to the rotation angle of the drive crank arm. Further, in a flexion angle range of the third joint portion when the user is in normal walking (walking on a flat floor), the rotational angular velocity of the driven crank arm is made slower than the rotational angular velocity of the drive crank arm so as to obtain a torque amplifying effect to make the toque (the drive torque of the third joint portion) transmitted to the driven crank arm greater than the output torque from the rotary actuator. According thereto, it is possible to increase the rotational angular velocity of the driven crank arm greater than the rotational angular velocity of the drive crank arm in a small range of the flexion angles of the third joint portion. Thereby, it is possible to increase only a small amount of amplified torque in the output torque of the rotary actuator needed to generate the assist force required in the normal walking. Thus, the required rotational angular velocity of the rotary actuator can be inhibited lower with only an increment on velocity so as to assure the controllability in a small range of the flexion angles of the third joint portion. Consequently, the weight of the rotary actuator can be reduced without impairing the walking assist function. Thereby, the inertial moment of the leg link around the first joint portion is reduced, and the load applied to the free leg when the user swings the free leg to the forward can be alleviated.

In the present invention, similar to Patent Document 1, the load transmit portion is composed of a seat member on which the user sits astride, the first joint portion is composed of an arc-shaped guide rail which is connected to the seat member and is longitudinal in an anteroposterior direction with the center of curvature located above the seat member, and a slider which is fixed at the upper portion of the first link portion and is movably engaged in the guide rail, the slider is engaged to a part of the guide rail which is positioned at a front side or a rear side to the connection line connecting the center of curvature of the guide rail and the joint shaft of the third joint portion, and it is desirable that the pivot portion of the connection link at which the drive crank arm is pivotally mounted is disposed opposite to the guide rail with respect to the connection line connecting the output shaft of the rotary actuator and the joint shaft of the third joint portion. According thereto, without providing a motion space for the drive crank arm and the connection link between the output shaft of the rotary actuator and the guide rail, the rotation shaft of the rotary actuator, namely, the center of gravity of the rotary actuator can be positioned nearby the guide rail. Moreover, a supporting force for supporting the weight of the user, namely, the force in the direction of decreasing the flexion angle of the third joint portion can be transmitted through the tension of the connection link. Different from transmitting the force through pushing, it is not necessary to enlarge the cross sectional area of the connection link to prevent it from buckling, which makes it possible to reduce the self weight of the connection link. Consequently, the inertial moment of the leg link around the first joint portion (around the center of curvature of the guide rail) can be further alleviated.

Moreover, it is necessary to provide an accessory member such as a battery in the first link portion. In this situation, as mentioned above, the pivot portion of the connection link at which the drive crank arm is pivotally mounted is disposed opposite to the guide rail with respect to the connection line connecting the output shaft of the rotary actuator and the joint shaft of the third joint portion. Accordingly, the accessory member can be disposed at a position at a portion of the first link portion where closer to the guide rail than to the connection line connecting the output shaft of the rotary actuator and the joint shaft of the third joint portion without interfering with the connection link. Thereby, the distance between the accessory member and the guide rail becomes shorter, and resultantly, the inertial moment of the leg link around the first joint portion can be prevented from increasing due to the weight of the accessory member as much as possible.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A walking assist device according to an embodiment of the present invention will be described hereinafter. As illustrated fromFIG. 1toFIG. 3, the walking assist device includes a seat member1as a load transmit portion on which a user P sits astride, a pair of left and right foot mounting portions2and2which are attached to user's left and right feet, respectively, and a pair of left and right leg links3and3disposed between the seat member1and the pair of left and right foot mounting portions2and2.

Each leg link3is composed of an upper first link portion5connected to the seat member1via a first joint portion4, a lower second link portion7connected to the foot mounting portion2via a second joint portion6, a middle third joint portion8connected to the first link portion5and the second link portion7in such a way that the first link portion5and the second link portion7can stretch and bend freely, and a drive mechanism9to drive the third joint portion8. Then, a force in the direction of stretching each leg link3is applied to each leg link3from the third joint portion8driven by the drive mechanism9to generate a supporting force which supports at least a part of the user's weight (hereinafter, referred to as assist force). The assist force generated in each leg link3is transmitted to the trunk of the user P via the seat member1to alleviate the load on the leg of the user P.

The seat member1is composed of a seat portion1awhere the user P sits, a support frame1b, and a waist supporter1c. The seat portion1ais of a saddle shape. The support frame1bis disposed below the seat portion1ato support the seat portion1a. The support frame1bis configured to extend upward behind the seat portion1a. The support frame1bhas an uprising portion at a rear end thereof. The waist supporter1cis fixed at the uprising portion. The waist supporter1cis provided with a holding portion1dof an arch shape to be held by the user P if necessary.

The first joint portion4for each leg link3has an arc-shaped guide rail41connected to the seat member1. Then, each leg link3is movably engaged with the guide rail41via a plurality of rollers43pivotally attached to a slider42which is fixed to the upper end of the first link portion5. Thereby, each leg link3swings in the anteroposterior direction around the center of curvature4aof the guide rail41and the anteroposterior swing fulcrum of each leg link3with respect to the first joint portion4functions as the center of curvature4aof the guide rail41.

Furthermore, the guide rail41is pivotally supported at the uprising portion formed at the rear end of the support frame1bof the seat member1via a spindle4bwhich is longitudinal in the anteroposterior direction. Thus, the guide rail41is connected to the seat member1, capable of swinging freely in the lateral direction. According thereto, each leg link3is allowed to swing in the lateral direction, which enables the user P to abduct the legs thereof. In addition, the anteroposterior swing fulcrum of each leg link3(the center of curvature4aof the guide rail41) and the lateral swing fulcrum (the spindle)4bare both located above the seat portion1a. Thereby, the seat member1can be prevented from inclining greatly both in the vertical direction and the lateral direction when the user P shifts the body weight thereof.

The first link portion5is disposed to be inclined backward. The slider42is engaged to a part of the guide rail41which is positioned at a rear side to the connection line connecting the center of curvature4aof the guide rail41and a joint shaft8aof the third joint portion8. Thereby, the swing stroke of the leg link3to the forward so as to follow the forward movement of a free leg of the user P can be assured without increasing the length of the guide rail to the forward direction too much.

Each foot mounting portion2has a shoe2aand a joint member2bprotruding upward from the inside of the shoe2a. The second link portion7of each leg link3is connected to the joint member2bvia the second joint portion6of a three-axis structure. As illustrated inFIG. 2, a pair of longitudinally disposed pressure sensors10and10, which detect loads applied to the metatarsophalangeal joint (MP joint) and the heel of each foot of the user P, respectively, are attached to the undersurface of an insole2cprovided in the shoe2a. Moreover, a 2-axis force sensor11is built into the second joint portion6. Detection signals from the pressure sensors10and the force sensor11are input into a controller12housed in the support frame1bof the seat member1. On the basis of the detection signals from the pressure sensors10and the force sensor11, the controller12performs a walking assist control by controlling the driving source9to drive the third joint portion8of the leg link3to generate the above-mentioned assist force.

The assist force is applied on a connection line (hereinafter, referred to as a reference line) joining a swing fulcrum4aof the leg link3with respect to the first joint portion4in the anteroposterior direction and a swing fulcrum of the leg link3with respect to the second joint portion6in the anteroposterior direction. In the walking assist control, the actual assist force applied on the reference line (accurately, a resultant force between the assist force and a force generated by the weights of the seat member1and each leg link3) is calculated based on detection values of forces in the two-axis direction detected by the force sensor11. Thereafter, on the basis of the stepping force detected by the pressure sensors10for each foot mounting portion2, a ratio of the stepping force of each foot with respect to the resultant force applied to both feet of the user P is calculated. Then, a desired control value of the assist force which should be generated in each leg link3is calculated by multiplying a predefined value of the assist force by the calculated ratio of the stepping force of each foot. Subsequently, the driving mechanism9is controlled so as to make the actual assist force calculated on the basis of the detection values by the force sensor11approximate to the desired control value.

The drive mechanism9is provided with a rotary actuator91mounted on the outer surface of the upper end portion of the first link portion5, a drive crank arm92disposed on an output shaft91bof the rotary actuator91, a driven crank arm93fixed to at the second link portion7concentrically to the joint shaft8aof the third joint portion8, and a connection link94with one end thereof pivoted at the drive crank arm92and the other end pivoted at the driven crank arm93. The rotary actuator91is composed of an electric motor provided with a reduction gear91a. As illustrated inFIG. 4, the connection link94is disposed in such a way that a connection line L2connecting a pivot portion94aof the connection link94at which the drive crank arm92is pivotally mounted and a pivot portion94bof the connection link94at which the driven crank arm93is pivotally mounted (hereinafter, referred to as a floating link line) obliquely crosses a connection line L1connecting the output shaft91bof the rotary actuator91and the joint shaft8aof the third joint portion8(hereinafter, referred to as a fixed link line).

When the floating link line L2is obliquely crossed with the fixed link line L1, a ratio between the rotational angular velocity of the driven crank arm93and the rotational angular velocity of the drive crank arm92varies according to the rotation angle of the drive crank arm92. In the present embodiment, when the flexion angle θ of the third joint portion8(the angle formed between the line passing through the third joint portion8and the center of curvature4aof the guide rail41and the line passing through the third joint portion8and the second joint portion6) is in the range of about 20° to 70°, the ratio of the angular velocity between the driven crank arm93and the drive crank arm92(the rotational angular velocity of the driven crank arm93/the rotational angular velocity of the drive crank arm92) is equal to or less then 1. When the ratio of the angular velocity is equal to or less then 1, the torque transmitted to the driven crank arm93, namely the drive torque of the third joint portion8becomes equal to or greater than the output torque of the rotary actuator91.

When the user P is in normal walking (walking on a flat floor), the flexion angle θ of the third joint portion8ranges from about 40° to 70°. Thus, in the range of the flexion angles of the third joint portion8when the user P is in normal walking, the rotational angular velocity of the driven crank arm93is slower than the rotational angular velocity of the drive crank arm92. As a result thereof, in normal walking, a torque amplifying effect is obtained to make the drive torque of the third joint portion8greater than the output torque of the rotary actuator91; consequently, the output torque of the rotary actuator91needed to generate the desired assist force is limited to the amount of the amplified torque only.

The telescopic velocity of the leg link3obtained by differentiating the length of the line segment between the swing fulcrum4aof the leg link3with respect to the first joint portion4and the second joint portion6(the length of the leg link) by the flexion angle θ of the third joint portion8slows down as the flexion angle θ decreases. In order to improve the controllability in a small range of the flexion angles θ, it is necessary to make the flexion angle θ vary faster. Accordingly, the required rotation velocity of the rotary actuator91would be greater, which makes it difficult to reduce the weight of the rotary actuator91. To solve this problem, in the present embodiment, the rotational angular velocity of the driven crank arm93is made faster than the rotational angular velocity of the drive crank arm92to gain the velocity increasing effect in the range of flexion angles θ equal to or less than about 20°. Thereby, the required rotational angular velocity of the rotary actuator91can be inhibited lower with only the increment on velocity so as to assure the controllability in a small range of the flexion angles θ.

Accordingly, in the present embodiment, according to the torque amplifying effect in normal walking and the velocity increasing effect in a small range of flexion angles θ, the weight of the rotary actuator91can be reduced without impairing a walking assist function thereof. Thereby, the inertial moment of the leg link3around the first joint portion4is reduced, and the load applied to the free leg when the user P swings the tree leg thereof to the forward can be alleviated.

In the present invention, the pivot portion94aof the connection link94at which the drive crank arm92is pivotally mounted is disposed opposite to the guide rail41of the first joint portion4with respect to the fixed link line L1. According thereto, without providing a motion space for housing the drive crank arm92and the connection link94between the output shall91bof the rotary actuator91and the guide rail41, the rotation shall91bof the rotary actuator91, namely, the center of gravity of the rotary actuator91can be positioned close to the guide rail41.

Moreover, the assist force supporting the weight of the user P, namely, the force in the direction of decreasing the flexion angle θ of the third joint portion8can be transmitted from the rotary actuator91to the third joint portion8through the tension of the connection link94. Different from transmitting the force through pushing, it is not necessary to enlarge the cross sectional area of the connection link94to prevent it from buckling, which makes it possible to reduce the self weight of the connection link94. Consequently, in addition to disposing the center of gravity of the rotary actuator91close10the guide rail41, the inertial moment of the leg link3around the first joint portion4(around the center of curvature4aof the guide rail41) can be further alleviated.

Moreover, as mentioned above, the pivot portion94aof the connection link94at which the drive crank arm92is pivotally mounted is disposed opposite to the guide rail41of the first joint portion4with respect to the fixed link line L1. Accordingly, a space can be assured in a portion of the first link portion5closer to the guide rail41than to the fixed link line L1without interfering with the connection link94. In the present embodiment, the accessory member13such as the battery or the like is disposed in the space. Thereby, the distance between the accessory member13and the guide rail41becomes shorter, and resultantly, the inertial moment of the leg link3around the first joint portion4can be prevented from increasing due to the weight of the accessory member13as much as possible. In addition, a cover51covering the accessory member13is attached to the first link portion5.

Though the embodiment of the present invention has been described as above, it is not limited thereto. For example, in the above-mentioned embodiment, the slider42is engaged to a part of the guide rail41which is positioned at a rear side than the connection line connecting the center of curvature4aof the guide rail41and the joint shaft8aof the third joint portion8. However, by bending the leg link3opposite to the one described in the above-mentioned embodiment in the lateral direction, it is acceptable to engage the slider42to a part of the guide rail41which is position at a front side than the connection line connecting the center of curvature4aof the guide rail41and the joint shaft8aof the third joint portion8. In this case, by disposing the pivot portion of the connection link94at which the drive crank arm92is pivotally mounted opposite to the guide rail41with respect to the connection line connecting the output shaft91bof the rotary actuator91and the joint shaft8aof the third joint portion8, similar effect can be obtained as in the above-mentioned embodiment.

In the embodiment mentioned above, the first joint portion4is configured to have the guide rail41of an arc shape and the swing fulcrum4aof each leg link3in the anteroposterior direction with respect to the first joint portion4is located above the seat member1. However, it is also possible to configure the first joint portion4to a simple-structured joint portion having a spindle in the lateral direction to pivotally support each leg link3so that the upper end portion thereof can freely swing in the anteroposterior direction. It is also acceptable to adopt a spring mounted around the waist of the user as the load transmit portion. Moreover, in order to assist the walking of a handicapped user whose one leg is crippled due to bone fracture or the like, it is possible to leave only one leg link of the left and right leg links3and3in the above-mentioned embodiment corresponded to the crippled leg of the user by removing the other.