Legged mobile robot

In a legged mobile robot (1), each leg (2) has at least a first joint (16) and a second joint (18, 20) located below the first joint in the gravitational direction, and the actuator that drives the second joint (54, 56) is located at least one of a position same as that of the first joint and a position (28) above the first joint in the gravitational direction. With this, it becomes possible to lighten the weight of the ground-contacting ends of the legs and thereby provide a legged mobile robot enabling reduction of the inertial forces occurring in the legs during moving, particularly during high-speed moving.

TECHNICAL FIELD

The present invention relates to a legged mobile robot, more particularly to the legs of a legged mobile robot.

BACKGROUND ART

Known technologies relating to legged mobile robots, particularly to the legs of legged mobile robots, include, for example, that set out in Japanese Patent No. 3293952. This prior art configuration secures driving forces necessary for walking by installing electric motors for driving the knee joints at the thigh links, installing electric motors for driving the ankle joints at the shank links, and driving speed reducers installed coaxially with the joint axes through belts.

When a legged mobile robot is caused to move, particularly when it is caused to move at high speed, large inertial forces are produced at the legs. It is therefore preferable to lighten the weight of the legs, particularly the ground-contacting ends thereof (ends contacting the floor surface; i.e., the distal ends), so as to reduce the inertial forces occurring in the legs during moving. However, the aforesaid prior art leaves room for improvement in the point of inertial force reduction because the weight of the ground-contacting ends of the legs is increased owing to the installation of the electric motors for driving the ankle joints at the shank links and the installation of the speed reducers coaxially with the ankle joint axes.

DISCLOSURE OF THE INVENTION

An object of the present invention is therefore to lighten the weight of the ground-contacting ends of the legs and thereby provide a legged mobile robot enabling reduction of the inertial forces occurring in the legs during moving.

In order to achieve the object, the present invention is configured, to have a legged mobile robot equipped with articulated legs such that it moves by driving each leg by an actuator associated therewith: characterized in that: each leg has at least a first joint and a second joint located below the first joint in the gravitational direction; and that the actuator that drives the second joint is located at least one of a position same as that of the first joint and a position above the first joint in the gravitational direction. Thus, since it is configured such that each leg has at least a first joint and second joint located below the first joint in the gravitational direction; and that the actuator that drives the second joint is located at least one of a position same as that of the first joint and a position above the first joint in the gravitational direction, it becomes possible to lighten the weight of the ground-contacting ends of the legs (distal end side, i.e., the side of the second joint) and thereby provide a legged mobile robot enabling reduction of the inertial forces occurring in the legs during moving, particularly during high-speed moving.

The present invention is further configured, such that at least one of an output shaft of the actuator that drives the second joint and an output shaft of a transmission element to which an output of the output shaft of the actuator is transmitted, is located coaxially with an axis of the first joint, and the second joint is connected to the output shaft located coaxially with the axis of the first joint to be driven through a rod. Thus, since it is configured such that at least one of an output shaft of the actuator that drives the second joint and an output shaft of a transmission element to which an output of the actuator is transmitted, is located coaxially with an axis of the first joint, and the second joint is connected to the output shaft located coaxially with the axis of the first joint to be driven through a rod made of a rigid body, in addition to the advantages mentioned above, even when the second joint and actuator or the second joint and transmission element are located apart from each other, driving force can be transmitted with good accuracy. Further, the first joint and second joint can be angularly adjusted independently.

The present invention is further configured, such that the second joint has rotation axes that are arranged in at least two different directions. Thus, since it is configured such that the second joint has rotation axes that are arranged in at least two different directions, smooth moving of the robot is made possible.

The present invention is further configured, such that the second joint is driven by a plurality of actuators and is connected to at least one of output shafts of the actuators and output shafts of transmission elements to which outputs of the actuators are transmitted, to be driven through a plurality of rods. Thus, since it is configured such that the second joint is driven by a plurality of actuators and is connected to at least one of output shafts of the actuators and output shafts of transmission elements to which outputs of the output shafts of the actuators are transmitted, to be driven through a plurality of rods, the second joint is driven by a plurality of actuators and is connected to at least one of output shafts of the actuators and output shafts of transmission elements to which outputs of the actuators are transmitted, to be driven through a plurality of rods, in addition to the advantages mentioned above, the driving of the second joint (more specifically, the ankle joints which require large driving force) can be conducted using the sum of the driving forces of a plurality of actuators, and the actuators that drive the second joint can be made compact.

The present invention is further configured, such that the rods are located to be spaced by prescribed distances from axes of the second joints. Thus, since it is configured such that the rods connecting the second joint and the outputs of the actuators (or the transmission elements to which their outputs are transmitted) are located to be spaced by prescribed distances from axes of the second joints, in addition to the advantages mentioned above, the second joint can be driven by a small force.

The present invention is further configured, such that the second joint is one among the joints that the legs have, that is located farthest toward a ground-contacting end. Thus, since it is configured such that the second joint is one among the joints that the legs have, that is located farthest toward a ground-contacting end, the distance between the ground-contact end of the leg and the second joint (ankle joint) can be reduced, thereby enabling to improve the stability of the robot.

BEST MODE OF CARRYING OUT THE INVENTION

A legged mobile robot according to an embodiment of the present invention will be explained with reference to the attached drawings in the following.

FIG. 1is a diagram schematically showing the legged mobile robot, more specifically biped walking robot, according to this embodiment with focus on the joint structure of the legs.

As illustrated, the biped walking robot (hereinafter called “robot”)1has six joints (shown as axes) installed in each of right and left legs2R,2L (R designating the right side and L designating the left side; hereinafter the same). The vertically upward six joints comprise, in order from the uppermost, a joint10R,10L (R designating the right side and L designating the left side; hereinafter the same) of the crotch (hip) for leg rotation (around the Z axis), a roll direction (around the X axis) joint12R,12L of the crotch (hip), a pitch direction (around the Y axis) joint14R,14L of the crotch (hip), a pitch direction joint16R,16L of the knee, a pitch direction joint18R,18L of the ankle, and a roll direction joint20R,20L of the ankle. In other words, the crotch joint (or hip joint) is composed of the joints10R(L),12R(L) and14R(L), the knee joint (the aforesaid first joint) of the joint16R(L), and the ankle joint (the aforesaid second joint) of the joints18R(L) and20R(L).

A foot22R, L is attached below the ankle joints18R(L),20R(L) and an upper body (main unit)24, inside of which is accommodated, inter alia, a control unit26composed of a microcomputer, is provided at the top. Further, the crotch joints10R(L),12R(L),14R(L) and the knee joint16R(L) are connected by a thigh link28R, L, and the knee joint16R(L) and the ankle joints18R(L),20R(L) are connected by a shank link30R, L.

In addition, as shown in the same drawing, a conventional six-axis force sensor (floor reaction force detector)34R(L) is attached between the ankle joints18,20R(L) and the ground-contact end of the foot22R(L) to measure the force components Fx, Fy and Fz of three directions and the moment components Mx, My and Mz of three directions so as to detect presence/absence of leg2R(L) landing (ground contact) and the floor reaction force (ground contact load) and the like acting on the leg2R(L) from the floor surface (not shown). Further, an inclination sensor36is mounted on the upper body24to detect inclination relative to the Z-axis (vertical direction (gravitational direction)) and the angular velocity thereof. Moreover, the electric motors that drive the respective joints are provided with rotary encoders (not shown) for detecting the amount of rotation thereof.

The outputs of the six-axis force sensors34R(L), the inclination sensor36and the like are input to the control unit26. Based on data stored in a memory (not shown) and the input detection values, the control unit26calculates control values for the electric motors (not shown in the drawing) that drive the respective joints.

Thus each of the right and left legs2R,2L of the robot1is imparted with six degrees of freedom and the legs as a whole can be imparted with desired movements to enable arbitrary moving in three-dimensional space by operating the motors that drive the 6×2=12 joints based on the control values calculated by the control unit26. Although arms and a head are connected to the upper body24, illustration thereof is omitted because the structures thereof are not directly related to the gist of this invention.

The legs2R,2L of the robot1will now be explained in detail with reference toFIG. 2and ensuing drawings. While the explanation will be made taking the right leg2R as an example, it should be noted that because the legs2R,2L are laterally symmetrical the following explanation also applies to the leg2L.

FIG. 2is a right side view showing in detail the leg2R shown schematically inFIG. 1. Illustration of the vicinity of crotch joints is omitted in the drawing. Further,FIG. 3is a rear view of the leg2R shown inFIG. 2.

As shown in the two drawings, a motor case50is mounted on the rear of the thigh link28R and an electric motor (hereinafter called “knee joint electric motor”)52for driving the knee joint16R is located inside an upper part of the motor case50. Further, a first electric motor (hereinafter called “first ankle joint electric motor”)54for driving the ankle joints18R,20R is located inside a lower part of the motor case50and a second electric motor (hereinafter called “second ankle joint electric motor”)56for driving the ankle joints18R,20R is located below the first ankle joint electric motor54. The first ankle joint electric motor54and second ankle joint electric motor56are arranged so as to orient their output shafts54osand56osoppositely in the lateral direction (Y-axis direction inFIG. 1).

Further, a speed reducer or reduction-gear mechanism (hereinafter called “knee joint speed reducer”)60is located on the front of the thigh link28R at a position opposite the aforesaid knee joint electric motor52. A pulley52pfastened to an output shaft52osof the knee joint electric motor52is connected through a belt52vto a pulley60pfastened to an input shaft60isof the knee joint speed reducer60, whereby the output of the knee joint electric motor52is transmitted to the knee joint speed reducer60. The knee joint speed reducer60is a known Harmonic Drive (registered trademark) and a detailed description thereof will be omitted.

In addition, a rod connector (hereinafter called “knee joint rod connector”)62is provided on an output shaft (not shown) of the knee joint speed reducer60and the upper end of a rod (hereafter called “knee joint rod”)64made of a rigid body is connected to the knee joint rod connector62to be rotatable in the pitch direction (around the Y-axis inFIG. 1).

On the other hand, the bifurcated lower end of the knee joint rod64is connected to a shank link side knee joint rod connector66formed at the upper end of the shank link30R, so as to be rotatable in the pitch direction. Thus, the shank link30R is connected to the knee joint speed reducer60through the knee joint rod connector62and knee joint rod64, whereby it is driven in the pitch direction by the output of the knee joint electric motor52. At such time, the rotation curve of the shank link30R is the axis16sof the aforesaid knee joint16R.

Two speed reducers70,72are located on the axis16sof the knee joint16R, one on either side (lateral side) of the knee joint16R. A pulley70pfastened to an input shaft70isof the speed reducer70is connected through a belt54vto a pulley54pfastened to an output shaft54osof the aforesaid first ankle joint electric motor54, whereby the output of the first ankle joint electric motor54is transmitted to the speed reducer70. The speed reducer70will be called a “first ankle joint speed reducer” hereinafter.

Further, a pulley72pfastened to an input shaft72isof the speed reducer72is connected through a belt56vto a pulley56pfastened to an output shaft56osof the aforesaid second ankle joint electric motor56, whereby the output of the second ankle joint electric motor56is transmitted to the speed reducer72. The speed reducer72will be called a “second ankle joint speed reducer” hereinafter. The first ankle joint speed reducer70and second ankle joint speed reducer72are both known Harmonic Drives whose bases (sections that do not rotate; not shown) are fastened to the shank link30R.

FIG. 4is a sectional view taken along line IV-IV ofFIG. 3, i.e., a sectional view of the knee joint16R.

As shown in the same drawing, the input shafts70is,72isand output shafts70os,72osof the first ankle joint speed reducer70and second ankle joint speed reducer72are all located coaxially with the axis16sof the knee joint16R. Further, a first ankle joint rod connector80is fastened to the output shaft70osof the first ankle joint speed reducer70, and the upper end of a first ankle joint rod82made of a rigid body is connected to the first ankle joint rod connector80to be rotatable in the pitch direction. Similarly, a second ankle joint rod connector84is fastened to the output shaft72osof the second ankle joint speed reducer72, and the upper end of a second ankle joint rod86made of a rigid body is connected to the second ankle joint rod connector84to be rotatable in the pitch direction.

Returning to the explanation ofFIG. 2andFIG. 3, a mount88is provided above the six-axis force sensor34R. A universal joint90equipped with rotation axes90aand90bin two different directions in the same plane is installed on the mount88. The universal joint90is connected to the lower end of the shank link30R, whereby it is connected to the aforesaid foot22R through the universal joint90, mount88and six-axis force sensor34R. The universal joint90will be called a “shank link connecting universal joint” hereinafter.

FIG. 5is a sectional view taken along line V-V inFIG. 3, i.e., a sectional view of the ankle joints18R,20R.

As shown in the same drawing, the shank link connecting universal joint90is equipped with two shafts90A and90B that intersect at right angles. The shaft90A is a roll direction (around the X-axis) rotating shaft that corresponds to the aforesaid joint20R and whose center of rotation is the rotation axis90a. Further, the opposite ends of the shaft90A are supported (fastened) by the mount88.

On the other hand, the shaft90B is a pitch direction (around the Y-axis) rotating shaft that corresponds to the aforesaid joint18R and whose center of rotation is the rotation axis90b. Further, the lower end of the bifurcated shank link30R is fastened to the opposite ends of the shaft90B. As a result, the ankle joints18R,20R are configured to be rotatable about any axis in a plane defined by the roll direction and pitch direction.

Returning to the explanation ofFIG. 2andFIG. 3, rearward of the shank link connecting universal joint90on the mount88are installed a smaller first rod universal joint92and second rod universal joint94. The lower end of the first ankle joint rod82is connected to the first rod universal joint92and the lower end of the second ankle joint rod86is connected to the second rod universal joint94.

The first rod universal joint92and second rod universal joint94will be explained in detail with reference toFIG. 5. The first rod universal joint92and second rod universal joint94are each equipped with two perpendicularly intersecting shafts92A and92B,94A and94B. The shafts92A,94A are both roll direction (around the X-axis) rotating shafts whose rotation axes92a,94aare located in the same plane as and parallel to the rotation axis90aof the aforesaid shank link connecting universal joint90. The lower end of the bifurcated first ankle joint rod82and the lower end of the second ankle joint rod86are respectively connected to the opposite ends of the shafts92A and94A.

Further, the shafts92B,94B are both pitch direction (around the Y-axis) rotating shafts whose rotation axes92b,94bare located in the same plane as and parallel to the rotation axis90bof the aforesaid shank link connecting universal joint90. The opposite ends of the shafts92B,94B are respectively supported (fastened) by the mount88. As a result, the lower ends of the ankle joint rods82,86are configured to be rotatable about any axis in a plane defined by the roll direction and pitch direction.

Thus, the ankle joints18R,20R are connected through the first ankle joint rod82and second ankle joint rod86to the first ankle joint speed reducer70and second ankle joint speed reducer72, which are transmission elements for transmitting the outputs of the first ankle joint electric motor54and second ankle joint electric motor56, whereby the ankle joints18R,20R are driven by the first ankle joint electric motor54and second ankle joint electric motor56.

Here the first ankle joint speed reducer70and second ankle joint speed reducer72are arranged coaxially with the axis16sof the knee joint16R located above the ankle joints18R,20R in the gravitational direction, and the first ankle joint electric motor54and second ankle joint electric motor56are located at the thigh link28R positioned still further above the knee joint16R, so that the weight of the ground-contacting end of the leg2R (distal end; i.e., the ankle joint18R,20R end) can be lightened to reduce the inertial force produced in the leg during moving, particularly during high-speed moving.

Moreover, since no speed reducer, electric motor or the like is located at the ankle joints18R,20R, the distance between the ground-contact end of the leg2R and the ankle joints18R,20R can be reduced to improve the stability of the robot1. Further, the distances between ground-contact end of the foot22R and the six-axis force sensor34R and between the six-axis force sensor34R and the ankle joints18R,20R can be shortened to enable accurate detection of the size and direction of the floor reaction force acting on the leg2R.

In addition, smooth moving of the robot1is possible because the ankle joints18R,20R are constituted by the shank link connecting universal joint90to provide the rotation axes90aand90bin two different directions.

Next, the driving operation of the ankle joints18R,20R will be explained with reference toFIG. 6andFIG. 7.FIG. 6A to 6Cis a set of schematic diagrams viewing the right leg2R from the right side and elucidating the driving operation of the ankle joints18R,20R.FIG. 7A to 7Cis a set of schematic diagrams viewing the right leg2R from behind and elucidating the driving operation of the ankle joints18R,20R.

An explanation follows. Taking the leg2R shown inFIG. 6Ato be in the initial state, when the second ankle joint speed reducer72is driven by the second ankle joint electric motor56(not shown) to rotate clockwise in the plane of the drawing sheet (i.e., clockwise when the leg2R is viewed from the right side) and the first ankle joint speed reducer70behind the second ankle joint speed reducer72is driven by the first ankle joint electric motor54(not shown) to rotate clockwise (counterclockwise when viewed from the side of the unshown leg2L on the left side), the second ankle joint rod connector84and second ankle joint rod86, and also the first ankle joint rod connector80and first ankle joint rod82, are driven upward to drive the foot22R so as to raise the heel (lower the toe), as shown inFIG. 6B.

Conversely, when the second ankle joint speed reducer72is driven by the second ankle joint electric motor56to rotate counterclockwise in the plane of the drawing sheet and the first ankle joint speed reducer70is driven by the first ankle joint electric motor54to rotate counterclockwise (clockwise when viewed from the side of the unshown leg2L on the left side), the second ankle joint rod connector84and second ankle joint rod86, and also the first ankle joint rod connector80and first ankle joint rod82, are driven downward to drive the foot22R so as to lower the heel (raise the toe), as shown inFIG. 6C. Thus, the ankle joints18R,20R are driven in the pitch direction (around the Y-axis) by driving the first ankle joint rod82and second ankle joint rod86in the same direction.

On the other hand, taking the leg2R shown inFIG. 7Ato be in the initial state, when the first ankle joint rod82is driven downward and the second ankle joint rod86is driven upward, the foot22R is driven to lower its left side (raise its right side), as shown inFIG. 7B.

Further, when the first ankle joint rod82is driven upward and the second ankle joint rod86is driven downward, the foot22R is driven to raise its left side (lower its right side), as shown inFIG. 7C. In other words, the ankle joints18R,20R are driven in the roll direction (around the X-axis) by driving the first ankle joint rod82and second ankle joint rod86in opposite directions.

Since the driving of the ankle joints18R,20R, which requires large driving force, can in this manner be conducted using the sum of the driving forces of two electric motors (the first ankle joint electric motor54and second ankle joint electric motor56), the ankle joint electric motors54,56can be made compact.

In addition, the first ankle joint rod82and second ankle joint rod86are, as shown inFIG. 3, located a prescribed distance d1sideways from the roll direction rotation axis90aof the shank link connecting universal joint90and, as shown inFIG. 2, located a prescribed distance d2rearward from the pitch direction rotation axis90bof the shank link connecting universal joint90. Namely, the ankle joints18R,20R can be driven by a small force because the points of force application (first rod universal joint92and second rod universal joint94) are located at positions a prescribed distance apart from the fulcrum (shank link connecting universal joint90).

Further, driving force can be transmitted with good accuracy even though the ankle joint speed reducers70,72are located apart from the ankle joints18R,20R because the first ankle joint speed reducer70and ankle joints18R,20R, and the second ankle joint speed reducer72and ankle joints18R,20R, are connected to be driven through the first ankle joint rod82and second ankle joint rod86, which are both rigid bodies.

This will be explained in detail with reference toFIG. 2. The second ankle joint electric motor56and second rod universal joint94, for example, cannot be connected by a rod made of a rigid body because their relative positions vary with driving of the knee joint16R. However, the relative positions of the axis16sof the knee joint16R and the second rod universal joint94do not vary with driving of the knee joint16R, so that by locating an electric motor or the output shaft of a speed reducer (transmission element) for transmitting the output thereof coaxially with the axis16sof the knee joint16R, they can be connected by a rod made of a rigid body.

In the foregoing, it is also conceivable, as shown inFIG. 8for example, to connect an electric motor102located at a thigh link100and an ankle joint104by a parallel linkage108made of a rigid body and having a fulcrum at a knee joint106. When connection is made by such a parallel linkage108, however, a problem arises in that it is difficult to angularly adjust the knee joint106and ankle joint104independently because the angle (bending angle) θ ankle of the ankle joint changes with change in the angle (bending angle) θ knee of the knee joint106. Specifically, defining the change in the angle θ knee of the knee joint106as θ move, θ ankle becomes approximately the sum of θ ankle and θ move. In other words, θ ankle changes by θ move.

On the other hand, in the legged mobile robot1according to this invention, change in the angle of the knee joint16R(L) has substantially no effect on the angles of the ankle joints18R(L),20R(L). To be precise, the relative angle between the aforesaid base (section fastened to the shank link30that does not rotate) and the input shaft70is,72ischanges when the angle of the knee joint16R(L) changes, so that the ankle joints18R(L),20R(L) are driven the pitch direction (around the Y-axis) by an angle reduced in proportion to the reduction ratio of the speed reducer70,72. Specifically, defining the change in the angle θ knee of the knee joint16R(L) as θ move, angle θ ankle of the ankle joint changes by approximately θ move/reduction ratio.

However, the reduction ratio of the speed reducers70,72ordinarily needs to be set large because, as mentioned earlier, large driving forces are required for driving the ankle joints. θ move/reduction ratio therefore becomes a very small value, so that the change in the angle of the knee joint16R(L) has substantially no effect on the angles of the ankle joints18R(L),20R(L). Moreover, since the rotational motion (rotational motion in the pitch direction) of the knee joint16R(L) is totally unrelated to the rotational motion in the roll direction (around the X-axis) of the ankle joints18R(L),20R(L), the motion of the knee joint16R(L) has no effect on roll direction motion of the ankle joints18R(L),20R(L). The knee joint16R(L) and the ankle joints18R(L),20R(L) can therefore be angularly adjusted independently.

As set out in the foregoing, the legged mobile robot according to this embodiment is configured such that in a legged mobile robot (robot)1equipped with articulated legs such that it moves by driving each leg by an actuator associated therewith so as to be equipped with the articulated legs2R(L) such that it moves by driving each leg by an actuator associated therewith, each leg has at least a first joint (knee joint16R(L)) and a second joint (ankle joint18R(L),20R(L)) located below the first joint in the gravitational direction; and the actuator that drives the second joint (first ankle joint electric motor54, second ankle joint electric motor56) is located at least one of a position same as that of the first joint and a position (thigh links28R(L)) above the first joint in the gravitational direction.

Further, it is configured such that, at least one of an output shaft (54os,56os) of the actuator that drives the second joint and an output shaft (70os,72os) of a transmission element (first ankle joint speed reducer70, second ankle joint speed reducer72) to which an output of the output shaft of the actuator is transmitted, is located coaxially with an axis (16s) of the first joint, and the second joint is connected to the output shaft located coaxially with the axis of the first joint to be driven through a rod (first ankle joint rods82, second ankle joint rods86).

Further, it is configured such that the second joint has rotation axes (90aand90b) that are arranged in at least two different directions.

Further, it is configured such that the second joint is driven by a plurality of actuators (first ankle joint electric motors54, second ankle joint electric motors56) and is connected to at least one of output shafts (54os,56os) of the actuators and output shafts (70os,72os) of transmission elements (first ankle joint speed reducers70, second ankle joint speed reducers72) to which outputs of the output shafts of the actuators are transmitted, to be driven through a plurality of rods (first ankle joint rods82, second ankle joint rods86).

Further, it is configured such that the rods are located to be spaced by prescribed distances (d1, d2) from axes (90a,90b) of the second joints.

Further, it is configured such that the second joint is one (ankle joints) among the joints that the legs have, that is located farthest toward a ground-contacting end.

Although explanation was made in the foregoing taking a biped walking robot equipped with two legs as an example of a legged mobile robot, the legged mobile robot can be one equipped with one or three or more legs.

Further, although the ankle joints are configured to be driven by two electric motors, it is possible to use one or three or more electric motor.

Further, although the speed reducers are located coaxially with the axes of the knee joints, the electric motor can be directly installed.

Further, the electric motors that drive the knee joints (or the transmission elements that transmit the outputs thereof) can be located coaxially with the axes of crotch joints and these be connected by rods.

Further, other than rods made of rigid bodies it is possible to use, for instance, push-pull cables and the like.

Further, the actuators used are not limited to electric motors and can be other kinds of actuators.

INDUSTRIAL APPLICABILITY

According to this invention, a legged mobile robot is configured such that legs are equipped with at least first joints and second joints located thereunder in the gravitational direction and actuators for driving the second joints are located at either the same position as the first joints or a position thereabove in the gravitational direction, so that the weight of the ground-contacting end of the legs (distal end; i.e., the second joint end) can be lightened to reduce the inertial forces produced in the legs during moving, particularly during high-speed moving.