Series-parallel multi-degree-of-freedom mechanical lower limb simulating human leg movement

Abstract

The invention relates to the field of humanoid robots, in particular to a series-parallel multi-degree-of-freedom mechanical lower limb simulating human leg movement. The invention aims to provide a series-parallel multi-degree-of-freedom mechanical lower limb simulating human leg movement, so that the pose control of the mechanical lower limb can be flexibly realized, the whole machine body is driven to move to obtain the desired movement and pose, and the balance of a connected robot and the like can be ensured in the movement process. According to the technical scheme, the series-parallel multi-degree-of-freedom mechanical lower limb simulating the leg movement of the human body is characterized in that the series-parallel multi-degree-of-freedom mechanical lower limb comprises a double-leg connecting structure connected with a mechanical upper limb and two mechanical single legs connected with the double-leg connecting structure through a first rotating pair capable of rotating around the horizontal axis; each mechanical single leg comprises a hip joint, a knee joint and an ankle joint which are sequentially connected from top to bottom.

Description

Technical Field

[0001] The present invention relates to the field of humanoid robots, and specifically to a hybrid multi-degree-of-freedom mechanical lower limb that imitates the movement of the human leg. Background Art

[0002] In recent years, due to their highly human-like form and motion ability, humanoid robots have shown broad application prospects in fields such as service, medical treatment, rescue, and industrial collaboration. As an ideal carrier for humans to interact with complex environments, humanoid robots need to possess motion flexibility, environmental adaptability, and energy efficiency similar to those of the human body. As the core motion unit, the mechanical lower limb directly determines the implementation effect of dynamic behaviors such as walking, running, and obstacle crossing.

[0003] However, the current research on humanoid robots is still in the exploratory stage, especially the lower limb structure design faces significant challenges. Traditional series mechanical legs such as CN119459928A have a large motion space but insufficient rigidity, making it difficult to support dynamic loads, and have fewer degrees of freedom, unable to achieve complex motions. Parallel structures have high rigidity but are limited by the lack of degrees of freedom, unable to reproduce the complex motion patterns of the coordinated work of multiple joints of the human hip, knee, and ankle, and there is still little research on them nowadays. In addition, existing research mostly focuses on a single motion scenario such as flat-ground walking, lacking adaptability to unstructured terrains such as stairs and slopes, and generally has problems such as high driving redundancy, high energy consumption, and low bionic motion accuracy, severely restricting the advancement of the practical application of humanoid robots.

[0004] In view of the above situation, there is an urgent need to provide a hybrid multi-degree-of-freedom mechanical lower limb that imitates the movement of the human leg. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the above background art and provide a hybrid multi-degree-of-freedom mechanical lower limb that imitates the movement of the human leg, so as to flexibly achieve the pose control of the mechanical lower limb, drive the entire body to move to obtain the desired actions and poses, and help the connected robots, etc., to maintain balance during the movement process.

[0006] The technical solution provided by the present invention is as follows:

[0007] A hybrid multi-degree-of-freedom mechanical lower limb that imitates the movement of the human leg, characterized in that: the hybrid multi-degree-of-freedom mechanical lower limb includes a double-leg connection structure connecting the mechanical upper limb and two mechanical single legs connecting the double-leg connection structure through a first rotating pair that can rotate around a horizontal axis, and each mechanical single leg includes a hip joint, a knee joint, and an ankle joint connected in sequence from top to bottom.

[0008] The hip joint includes a connecting housing with its top end connected to the first rotating pair and an open bottom end, and a driving body installed inside the connecting housing. The driving body includes a 3RRR parallel spherical mechanism with three driving parts and an end moving platform located at the bottom end of the hip joint and driven by the 3RRR parallel spherical mechanism.

[0009] The knee joint includes a thigh housing with its top end connected to the end moving platform, and two push rod branches and two moving branches that are vertically arranged with their top ends connected to the thigh housing. The bottom ends of the two moving branches are commonly connected to an end rotating rod. The two push rod branches and the two moving branches are symmetrically arranged, and the bottom ends of the two push rod branches are commonly connected to a horizontally arranged seventh transmission pair rotating shaft. The end rotating rod and the seventh rotating pair rotating shaft cooperate to form a seventh rotating pair.

[0010] The push rod branch includes a push rod motor fixedly installed inside the thigh housing with its push rod extending downward, a push rod sleeve fixed on the push rod motor and coaxially covering the outside of the push rod to perform sliding cooperation with the push rod, a third connecting rod with one end rotatably cooperating with the front end of the push rod through a fifth rotating pair, and an end rotating rod with its side rotatably cooperating with the other end of the third connecting rod through a sixth rotating pair. The axes of the two fifth rotating pairs and the two sixth rotating pairs in the two push rod branches are horizontally arranged and parallel to each other and symmetric with respect to the axis of the seventh transmission pair rotating shaft; the axes of the two sixth rotating pairs are parallel and arranged with respect to the axis of the fifth transmission pair rotating shaft.

[0011] The moving branch includes a slide rod that can be vertically slidably positioned on the thigh housing through a first moving pair and has its bottom end connected to the seventh rotating pair. The first moving pair includes a slide rail vertically arranged on the thigh housing and the slide rod slidably inserted into the slide rail; an adjusting screw passes through the slide rail and then is threadedly engaged with the slide rod to fix the slide rod to the thigh housing, thereby adjustably determining the thigh length.

[0012] The ankle joint includes a calf housing with its top end connected to the end rotating rod, two rollers rotatably arranged inside the calf housing around a horizontal axis and respectively driven by roller motors, a foot connected to the bottom end of the calf housing through a second Hooke's joint, and four series elastic drive units and two parallel spring buffer units arranged between the calf housing and the foot.

[0013] Two of the four series elastic drive units are respectively connected to the left and right sides of the two drums and the front end of the foot, and the other two are respectively connected to the left and right sides of the two drums and the rear end of the foot; in the horizontal plane projection, the connecting line of the two connection points of the front end of the foot connecting the two series elastic drive units and the connecting line of the two connection points of the rear end of the foot connecting the two series elastic drive units are respectively located on the front and rear sides of the axis of the second Hooke hinge; and, the connecting line of the two connection points of the left side of the foot connecting the two series elastic drive units and the connecting line of the two connection points of the right side of the foot connecting the two series elastic drive units are respectively located on the left and right sides of the axis of the second Hooke hinge.

[0014] The series elastic drive unit includes an elastic element and two pulling wires connected to both ends of the elastic element. One pulling wire is connected to the foot, and the other pulling wire is connected to the drum; in the two series elastic drive units connected to the front end of the foot, after the other ends of the two pulling wires are respectively wound around the two drums, they are respectively connected to the two pulling wires in the two series elastic drive units connected to the rear end of the foot.

[0015] The parallel spring buffer unit includes a first Hooke hinge connected in sequence between the calf housing and the foot, a buffer spring buffer rod sleeved, a buffer sleeve slidably matched with the buffer rod, and a ball hinge;

[0016] The two drum motor shafts are installed diagonally and in the opposite direction inside the calf housing and their axes are parallel to each other; the two pulling wires of the two series elastic drive units connecting the front end of the foot are respectively wound and connected to the drums on the same side of the calf housing, and the two series elastic drive units connecting the rear end of the foot are respectively wound and connected to the drums on the opposite sides of the calf housing.

[0017] The beneficial effects of the present invention are:

[0018] The present invention can realize the function of the hybrid mechanical lower limb imitating the movement of the human leg, with good support performance and high load-bearing capacity. Through the cooperation of various degrees of freedom, the pose control of the mechanical lower limb can be flexibly realized, driving the whole body to move to obtain the desired actions and poses, which is helpful for the connected robots and the like to ensure balance during the movement. In addition, the housing material is designed with hollowing out, which can reduce the material cost, reduce the weight of the mechanical lower limb, reduce the support pressure while ensuring the movement accuracy and stiffness, and the drive material selection is more flexible. Description of the Drawings

[0019] Figure 1 It is a schematic structural diagram of the present invention when walking.

[0020] Figure 2 is Figure 1 A three-dimensional schematic diagram of the double-leg connection structure in the shown hybrid mechanical lower limb.

[0021] Figure 3 is Figure 1 a schematic three-dimensional structure diagram of a mechanical single leg in the shown series-parallel mechanical lower limb.

[0022] Figure 4 is Figure 3 a schematic three-dimensional structure diagram of the driving body of the hip joint in

[0023] Figure 5 is Figure 2 a schematic three-dimensional structure diagram of the knee joint in the shown mechanical single leg.

[0024] Figure 6 is Figure 2 a schematic three-dimensional structure diagram of the ankle joint in the shown mechanical single leg.

[0025] Reference numerals:

[0026]

[0027] Detailed implementation manners

[0028] The present invention will be further described below with reference to the embodiments shown in the drawings.

[0029] Refer to Figures 1 to 3 ; The series-parallel multi-degree-of-freedom mechanical lower limb imitating human leg movement provided by the present invention includes a two-leg connection structure 1 and two mechanical single legs 2. The two-leg connection structure 1 is used to connect a mechanical upper limb; each mechanical single leg 2 includes a hip joint 3, a knee joint 4, and an ankle joint 5 connected in sequence from top to bottom, and the two mechanical single legs 2 are connected to the two-leg connection structure through a first rotating pair 11; the axis of the first rotating pair is horizontally arranged and parallel to the front-back direction of the human body.

[0030] The hip joint (prior art) includes a connection housing 12 connected to the top of the first rotating pair and a driving body installed in the connection housing; the driving body includes a 3RRR parallel spherical mechanism with three driving motors 31 and an end moving platform 311 driven by the 3RRR parallel spherical mechanism; the end moving platform 311 is located at the bottom end of the hip joint.

[0031] As Figure 4As shown, the driving body includes a hip joint housing 312, a 3RRR parallel spherical mechanism installed inside the hip joint housing, and an end moving platform 311. It can be seen from the figure that the 3RRR parallel spherical mechanism contains three worm and worm gear pairs with the same structure. Among them, the three worms 32 can all be rotatably installed on the hip joint housing through the second rotating pair 33 (i.e., bearings) and their axes are horizontally arranged, and are respectively driven by a driving motor 31 through a coupling (the three driving motors are installed on two adjacent sides of the hip joint housing, and two of the driving motors are installed on the same side). The three worm gears 34 respectively meshing with the three worms are all fastened to their respective worm shafts, and the worm shafts are all hollow shafts; the three worm gears are arranged vertically one above the other and the axes of the worm gears are all vertically arranged (the three worm shafts are all vertically arranged, with the top fixed to the worm gear and the bottom extending downward), and the annular support frame 35 fixed to the inner side of the side wall of the hip joint housing supports the end face of the lowermost worm gear through the provided axial bearing, while the top plane of the hip joint housing abuts against the end face of the uppermost worm gear, so as to realize the up and down limit of the three worm gears; in addition, a T-shaped fixed shaft is vertically fixed to the top plane of the hip joint housing, and the T-shaped fixed shaft penetrates downward into the inner cavity of the worm shaft of the uppermost worm gear, and the other two worm shafts are coaxially sleeved outside the worm shaft of the uppermost worm gear in sequence, so as to realize the radial positioning of the three worm gears. It can also be seen from the figure that the bottoms of the three worm shafts all extend downward through the inner ring surface of the annular support frame and are suspended below the annular support frame, and the bottom end faces 36 of the three worm shafts are respectively fixed with a first connecting rod 37, and the hanging end of each first connecting rod is connected to one end of a second connecting rod 39 through a third rotating pair 38 formed by hinge; the other ends of the three second connecting rods 39 are respectively connected to the same annular end moving platform 311 through a fourth rotating pair 310 formed by hinge (the three hinge points where the end moving platform is connected to the second connecting rods are symmetric with respect to the axis of the end moving platform). Obviously, when the three driving motors rotate at the same speed or differentially, two driving motors rotate at the same speed or differentially, or one driving motor rotates, the axis of the end moving platform can be respectively driven to swing at different angles, and / or the end moving platform can be driven to swing around its axis at different angles.

[0032] As Figure 5 shown: The knee joint 4 includes a thigh housing 41, two push rod branches, two moving branches, and an end rotating rod 46; the top of the thigh housing is connected to the end moving platform 311, the tops of the two push rod branches and the tops of the two moving branches are both connected to the thigh housing and are vertically arranged; the two push rod branches and the two moving branches are symmetrically arranged with each other, and the bottoms of the two push rod branches are jointly connected to a horizontally arranged seventh transmission pair rotating shaft, and the bottoms of the two moving branches are jointly connected to the end rotating rod 46; the end rotating rod and the seventh rotating pair rotating shaft cooperate to form a seventh rotating pair 48.

[0033] The two push rod branches include a push rod motor 42, a push rod sleeve 43, a push rod 44, a fifth rotating pair 410, a third connecting rod 45, and a sixth rotating pair 47; the push rod motor 42 is fixedly installed inside the thigh housing 41 and its push rod 44 extends downward; the push rod sleeve 43 is fixedly installed on the push rod motor 42 and coaxially covers the outside of the push rod, so that the push rod 44 is in sliding fit with the push rod sleeve 43. The front end of the push rod 44 is rotationally fitted with one end of the third connecting rod 45 through the fifth rotating pair 410, and the other end of the third connecting rod 45 is connected to the side surface of the end rotating rod 46 through the sixth rotating pair 47. The axes of the two fifth rotating pairs and the two sixth rotating pairs in the two push rod branches are horizontal and arranged parallel to each other, and are also symmetric about the axis of the seventh transmission pair rotating shaft.

[0034] The two moving branches include a seventh rotating pair 48, a sliding rod 49, an adjusting screw 411, a slide rail 412, and a first moving pair 413. The bottom end of the sliding rod 49 is rotationally fitted with the front surface of the end rotating rod 46 through the seventh rotating pair 48. The slide rail 412 is fixedly arranged on the thigh housing 41, and the sliding rod is slidably inserted into the slide rail to form a first moving pair 413; the adjusting screw 411 passes through the slide rail and then is in threaded fit with the sliding rod to fix the sliding rod and the thigh housing, so as to adjust and determine the thigh length.

[0035] The two push rod branches are vertically installed, and the bottoms of the two push rod branches are symmetrically installed relative to the axis of the seventh rotating pair 410. The two moving branches are vertically installed and symmetrically installed relative to the end rotating rod 46.

[0036] The same-direction telescoping of the two push rod branches can realize the translational degree of freedom of the end rotating rod 46, and the opposite-direction telescoping of the two push rod branches can realize the rotational degree of freedom of the end rotating rod 46.

[0037] As Figure 6 shown: The ankle joint 5 includes a calf housing 51, two rollers 52, two roller motors 53, four series elastic drive units, two parallel spring buffer units, a second Hooke hinge 511, and a foot 59; the top end of the calf housing is connected to the end rotating rod 46. The two rollers 52 horizontally arranged inside the calf housing are each coaxially connected to a roller motor 53, and the axes are parallel and vertically aligned and installed inside the calf housing 51; the foot 59 is connected to the bottom end of the calf housing through the second Hooke hinge 511; the four series elastic drive units and the two parallel spring buffer units are arranged between the calf housing and the foot.

[0038] Two of the four series elastic drive units are connected to the left and right sides of the front end of the foot and the two drums, and the other two are connected to the left and right sides of the rear end of the foot and the two drums. In the horizontal plane projection, the connection line of the two connection points of the two series elastic drive units connected to the front end of the foot and the connection line of the two connection points of the two series elastic drive units connected to the rear end of the foot are respectively located on the front and rear sides of the axis of the second Hooke hinge; moreover, the connection line of the two connection points of the two series elastic drive units connected to the left side of the foot and the connection line of the two connection points of the two series elastic drive units connected to the right side of the foot are respectively located on the left and right sides of the axis of the second Hooke hinge.

[0039] The series elastic drive unit includes an elastic element 54 and two pulling wires connected to both ends of the elastic element. One pulling wire is connected to the foot, and the other pulling wire is connected to the drum; among the two series elastic drive units connected to the front end of the foot, after the other ends of the two pulling wires are respectively wound around the two drums for several turns, they are respectively connected to the two pulling wires of the two series elastic drive units connected to the rear end of the foot (or directly used as the pulling wires of the series elastic drive units connected to the rear end of the foot).

[0040] The parallel spring buffer unit includes a buffer guide rod 55, a buffer spring 56, a buffer sleeve 57, a ball hinge 58, and a first Hooke hinge 510; the end of the buffer guide rod 55 is connected to the lower leg housing 51 through the first Hooke hinge; the buffer guide rod 55 is slidably matched with the buffer sleeve 57, the buffer spring 56 is sleeved on the buffer guide rod and its two ends respectively abut against the front end of the buffer sleeve and the first Hooke hinge, and the end of the buffer sleeve 57 is connected to the foot 59 through the ball hinge 58.

[0041] The drum motor is coaxially connected and installed with the drum; the two drum motors 53 are installed diagonally and reversely ( Figure 5 In the figure, the arrow indicates the front side of the foot; it can be seen that the upper drum motor is installed on the left side of the drum, and the lower drum motor is installed on the right side of the drum) inside the lower leg housing 51. The two pulling wires of the two series elastic drive units connecting the front end of the foot 59 are respectively wound and connected to the drum 52 on the same side of the lower leg housing (from Figure 6 it can be seen that the two ends of the pulling wire of one series elastic drive unit are respectively connected to the upper drum and the right side of the foot, and the upper drum is also located on the right side of the lower leg housing; the two ends of the pulling wire of the other series elastic drive unit are respectively connected to the lower drum and the left side of the foot, and the lower drum is also located on the left side of the lower leg housing). The two series elastic drive units connecting the rear end of the foot 59 are respectively wound and connected to the drum 52 on the opposite side of the lower leg housing (from Figure 6It can be known that: the two ends of the pulling line of a series elastic drive unit are respectively connected to the upper roller and the left side of the foot, and the upper roller is installed on the right side of the lower leg housing; the two ends of the pulling line of the other series elastic drive unit are respectively connected to the lower roller and the right side of the foot, and the lower roller is installed on the left side of the foot. The horizontal plane projections of the two parallel spring buffer units are parallel to each other.

[0042] When the two roller motors 53 rotate freely, they can pull the four series elastic drive units to achieve two rotational degrees of freedom of the foot 59 (the degrees of freedom of rotating around the two rotating shafts of the second Hooke joint 511 respectively). Specifically: when the two roller motors rotate in the same direction, the foot swings up and down on the front and back sides; when the two roller motors rotate in the opposite direction, the foot swings up and down on the left and right sides.

[0043] Working principle

[0044] This hybrid mechanical lower limb can achieve the degrees of freedom required for bionic human leg movement, including three rotational degrees of freedom of the hip joint, one rotational degree of freedom and one translational degree of freedom of the knee joint, and two rotational degrees of freedom of the ankle joint. The differential rotation of two of the worm and worm gear pairs in the hip joint controls two rotational degrees of freedom, and the three worm and worm gear pairs together control the overall axial rotational degree of freedom; the same-direction and same-speed telescoping of the two push rod branches in the knee joint can achieve one translational degree of freedom, and the differential telescoping can achieve one rotational degree of freedom; the same-direction or opposite-direction rotation of the two roller motors in the ankle joint can pull the four series elastic drive units to achieve two rotational degrees of freedom of the ankle joint around the two rotating shafts of the second Hooke joint. When the degrees of freedom movements of each part cooperate with each other, precise movement control of the mechanical single leg can be achieved. When two mechanical single legs cooperate with each other, flexible movement of the mechanical lower limb can be achieved, ensuring the balance of the fuselage movement and realizing the function of bionic human leg movement.

Claims

1. A hybrid multi-degree-of-freedom mechanical lower limb imitating human leg movement, characterized in that: The hybrid multi-degree-of-freedom mechanical lower limb comprises a double-leg connection structure (1) connected to a mechanical upper limb, and two mechanical single legs (2) connected to the double-leg connection structure via a first rotation pair (11) that can rotate around a horizontal axis, wherein the mechanical single leg (2) comprises a hip joint (3), a knee joint (4) and an ankle joint (5) that are connected in sequence from top to bottom.

2. The hybrid multi-degree-of-freedom mechanical lower limb imitating human leg movement according to claim 1, wherein: The hip joint (3) comprises a connection shell (12) with a top end connected to a first rotation pair (11) and an open bottom end, and a driving body installed in the connection shell. The driving body comprises a 3RRR parallel spherical mechanism with three driving motors (31) and an end moving platform (311) located at the bottom end of the hip joint and driven by the 3RRR parallel spherical mechanism.

3. The hybrid multi-degree-of-freedom mechanical lower limb imitating human leg movement according to claim 2, characterized in that: The knee joint (4) comprises a thigh shell (41) whose top end is connected to the terminal moving platform (311) and two push rod branches and two movable branches which are connected to the thigh shell at the top end and are arranged vertically; the bottom ends of the two movable branches are commonly connected to the terminal rotating rod (46), the two push rod branches and the two movable branches are arranged symmetrically with each other and the bottom ends of the two push rod branches are commonly connected to the seventh transmission secondary shaft which is arranged horizontally, and the terminal rotating rod cooperates with the seventh rotating secondary shaft to form the seventh rotating pair (48).

4. The hybrid multi-degree-of-freedom mechanical lower limb imitating human leg movement according to claim 3, characterized in that: The push rod branch includes a push rod motor (42) fixedly mounted inside the thigh shell (41) and having a push rod (44) extending downward, a push rod sleeve (43) fixed to the push rod motor (42) and coaxially covering the outside of the push rod so as to slide with the push rod, a third connecting rod (45) whose one end is rotationally matched with the front end of the push rod through a fifth rotating pair (410), and a terminal rotating rod (46) whose side is rotationally matched with the other end of the third connecting rod through a sixth rotating pair (47) whose axis is parallel to the fifth rotating pair. The axes of the two fifth rotating pairs and the two sixth rotating pairs in the two push rod branches are horizontal and parallel to each other and symmetrical to the axis of the seventh transmission pair shaft.

5. The hybrid multi-degree-of-freedom mechanical lower limb imitating human leg movement according to claim 4, characterized in that: The movable branch includes a slide rod (49) which can be vertically slidably positioned on the thigh shell through a first movable pair (413) and the bottom end of which is connected to the seventh rotating pair. The first movable pair includes a slide rail (412) vertically arranged on the thigh shell and the slide rod slidably inserted in the slide rail; the adjusting screw (411) passes through the slide rail and then cooperates with the slide rod thread to fix the slide rod to the thigh shell, thereby adjusting the thigh length.

6. The hybrid multi-degree-of-freedom mechanical lower limb imitating human leg movement according to claim 5, wherein: The ankle joint (5) comprises a calf shell (51) whose top end is connected to the terminal rotating rod, two rollers (52) arranged in the calf shell so as to be rotatable around a horizontal axis and driven by roller motors (53), a foot (59) connected to the bottom end of the calf shell via a second Hooke's joint (511), and four series elastic drive units and two parallel spring buffer units arranged between the calf shell and the foot.

7. The hybrid multi-degree-of-freedom mechanical lower limb imitating human leg movement according to claim 6, characterized in that: Two of the four series elastic drive units are respectively connected to the left and right sides of the front end of the foot and the two drums, and the other two are respectively connected to the left and right sides of the rear end of the foot and the two drums; in the horizontal plane projection, the connecting line of the two connection points of the two series elastic drive units connected to the front end of the foot and the connecting line of the two connection points of the two series elastic drive units connected to the rear end of the foot are respectively located on the front and rear sides of the axis of the second Hooke hinge; and, the connecting line of the two connection points of the two series elastic drive units connected to the left side of the foot and the connecting line of the two connection points of the two series elastic drive units connected to the right side of the foot are respectively located on the left and right sides of the axis of the second Hooke hinge.

8. The hybrid serial-parallel multi-degree-of-freedom mechanical lower limb imitating human leg movement according to claim 7, characterized in that: The series elastic drive unit includes an elastic element (54) and two pull wires connected to both ends of the elastic element. One pull wire is connected to the foot, and the other pull wire is connected to the drum; in the two series elastic drive units connected to the front end of the foot, after the other ends of the two pull wires are respectively wound around the two drums, they are respectively connected to the two pull wires in the two series elastic drive units connected to the rear end of the foot.

9. The hybrid multi-degree-of-freedom mechanical lower limb imitating human leg movement according to claim 8, characterized in that: The parallel spring buffer unit includes a first hinge Hooke hinge (510) sequentially connected between the calf housing and the foot, a buffer guide rod (55) sleeved with a buffer spring (56), a buffer sleeve (57) slidably matched with the buffer guide rod, and a ball hinge (58).

10. The hybrid multi-degree-of-freedom mechanical lower limb imitating human leg movement according to claim 9, characterized in that: The two drum motors (53) are installed diagonally and reversely inside the calf housing (51) and their axes are parallel to each other; the two pull wires of the two series elastic drive units connected to the front end of the foot are respectively wound and connected to the drums on the same side of the calf housing, and the two series elastic drive units connected to the rear end of the foot are respectively wound and connected to the drums on the opposite sides of the calf housing.

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