JP2000166997A - Walking aid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply help daily walking operation by controlling the power of a power means to help the movement of both legs the movement of both of the 1egs is detected. SOLUTION: When a user raises his/her right leg in order to start walking, e.g. an auxiliary device 2 is rotated in a direction A to turn a gear 4, a chain 3 and gears 5 and 6. Then, a rotation detecting sensor 7 detects the elevation of his/her right leg and outputs a signal corresponding to the rotation speed to a control part 9. Then, a motor 8 is rotated in a direction B. Consequently the gears 6 and 5, the chain 4 and the gear 4 and the gear 4 are rotated to help the movement of his/her right leg in the direction A. When the movement of the right leg is stopped, the motor is also stopped. Then help is stopped and the right leg is lowered by its dead weight. His/her left leg is also helped to simply help walking operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a walking assist device for assisting a person's walking operation.

[0002]

2. Description of the Related Art When a person's behavioral ability is reduced due to injury, illness, aging, etc., daily activities such as walking are accompanied by pain and difficulty, and people seek assistance. People who cannot walk or who have difficulty walking have walking assist devices such as wheelchairs and crutches. There are also bicycles with auxiliary power for healthy persons.

[0003]

However, those who can walk, but who suffer a little pain, can use a wheelchair,
The use of walking aids such as crutches, on the contrary, was cumbersome. Further, a bicycle with auxiliary power can exert its effect in a normal use range, but cannot exert its effect in a place where there are stairs, for example.

The present invention has been made in view of the above points, and an object of the present invention is to provide a walking assist device which can easily assist a daily walking operation.

[0005]

In order to achieve the above object, a walking assist device according to a first aspect of the present invention includes a power means having a power for assisting the movement of both feet of a human, and a movement detecting means for detecting the movement of the both feet. It is characterized by comprising detecting means, and control means for controlling the power of the power means so as to assist the movement of both feet when the movement of both feet is detected by the detecting means.

[0006]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a diagram showing a configuration of a walking assist device 100 according to a first embodiment of the present invention.

The walking assist device 100 includes a fixture 1 for attaching the device to a user's body, an assist device 2 attached to the left and right thighs of the user, and one end of the assist device 2. And a chain 3 for transmitting the power of the motor 8 to the left and right auxiliary devices 2 via the gears 4 and 5.

The motor 8 has a gear 18, and the gear 6 is meshed with the gear 18, and the gear 6 and the gear 5 have the same rotating shaft. A gear 17 meshes with the gear 6, and the gear 17 is attached to a rotation shaft of a sensor unit of the rotation detection sensor 7 to detect a rotation state of the gear 17. further,
A control unit 9 that controls driving of the rotation detection sensor 7 and the motor 8 and a battery 10 that supplies power to the rotation detection sensor 7 and the control unit 9 are provided.

The rotation shaft of the gear 4 rotatably connects the auxiliary device 2 and the fixture 1, and the rotation shafts of the gears 5 and 6 are attached to the fixture 1. The gear 4 and the gear 5 are connected via the chain 3. When the rotation detection sensor 7 detects the rotation, it outputs a signal corresponding to the rotation number to the control unit 9.

FIG. 2 is a diagram showing the configuration of the control unit 9. The control unit 9 includes an input / output interface 91 for inputting and outputting signals, and a ROM 92 for storing a control program.
A RAM 93 that is a work area for executing a control program; and a CPU 94 that controls the RAM 93, the ROM 92, and the input / output interface 91. The ROM 92 stores an angle detection program 95 for detecting an angle of the thigh with respect to the torso of the user in the front-rear direction based on a signal corresponding to the number of rotations of the gear 6 output from the rotation detection sensor 7.

When a signal corresponding to the rotation speed of the gear 6 output from the rotation detection sensor 7 is input to the input / output interface 91, the CPU 94 receives an angle detection program 95
To detect the angle of the thigh with respect to the torso of the user in the front-rear direction. Then, it is determined whether or not to drive the motor 8 based on the detected angle, and a signal corresponding to the determination result is output to the motor 8 via the input / output interface 91. The motor 8 is driven by a signal input from the CPU 94.

The CPU 94 includes a constant current drive control for controlling a predetermined constant current to flow through the motor 8, a constant voltage drive control for controlling a predetermined constant voltage to be supplied to the motor 8, and a predetermined pulse to the motor 8. There are three control methods of PWM (pulse width modulation) drive control for periodically supplying a pulse having a width. In the present embodiment, PWM drive control is performed. still,
The predetermined value of the constant current in the constant current drive control, the predetermined value of the constant voltage in the constant voltage drive control, and the predetermined value of the pulse width in the PWM drive control are all variable. By controlling, the CPU 94 can gradually increase or decrease the driving force of the motor 8.

FIG. 3 is a diagram showing a situation where the user steps on the right foot. The direction A in FIG. 3 is the direction of rotation of the foot when the user steps on the foot (counterclockwise),
The direction B in FIG. 3 is the direction of rotation of the foot when the user pulls back the foot (clockwise).

The following (1) to (16) show the operating state of the walking assist device 100 when the user steps on the right foot from the stopped state. (1) The user starts raising the right foot. (2) The auxiliary device 2 attached to the thigh of the user rotates (A direction). (3) The gear 4, the chain 3, the gear 5, and the gear 6 rotate (A direction). (4) The rotation detection sensor 7 detects rotation (elevation of the right foot). (5) The rotation detection sensor 7 outputs a signal corresponding to the number of rotations to the control unit 9. (6) The electric power preset by the control unit 9 is supplied to the motor 8. (Note that the preset electric power does not exceed the power of the user and has such a magnitude that the rotation of the motor 8 can be easily stopped by the power of the user.) (7) The motor 8 rotates (direction B). . (8) The gear 6, gear 5, chain 3 and gear 4 rotate (A direction). (9) Assist the movement of the right foot in the A direction. (10) The user stops the movement of the right foot. (11) The rotation of the gear 6, the gear 5, the chain 3, and the gear 4 stops. (12) The rotation detection sensor 7 detects the stop of the rotation. (13) A signal corresponding to the rotation stop is output from the rotation detection sensor 7 to the control unit 9. (14) The control unit 9 stops driving the motor 8. (15) The movement of the right foot is not assisted in the A direction. (16) The right foot falls under its own weight The operation state of the walking assist device 100 when the left foot is stepped on is the same as in the above-mentioned (1) to (16), and a description thereof will be omitted.

FIG. 4 is a flowchart showing a program executed by the CPU 94 to operate the walking assist device 100. This program is executed in parallel for each of the left and right feet. This program is C
The processing is executed until the power from the battery 10 is not supplied to the PU 94.

First, when a signal corresponding to the number of rotations of the gear 6 output from the rotation detection sensor 7 is input to the input / output interface 91, an angle detection program 95 is executed, and the thigh of the thigh relative to the torso of the user is executed. The angle in the front-back direction is detected (step S1).

Next, the angle detected in step S1 is differentiated with respect to time (step S2).
It is determined whether or not the angle detected in step 1 is increasing in the direction in which the foot is stepped forward (step S3). If the angle is increasing in the direction in which the foot is stepped forward, the angle is increased. A pulse having a predetermined pulse width is periodically supplied to the motor 8 in order to assist walking of the foot (step S
4) On the other hand, if the angle does not increase in the direction in which the foot is stepped forward, the supply of the pulse to the motor 8 is stopped, and the driving of the motor 8 is stopped (step S).
5). Thereafter, the process returns to step S1.

The force for assisting the foot by the motor 8 is controlled so as to be smaller than the force that the user originally has to step forward on the foot when walking.
The driving force of the motor 8 is controlled so as not to exceed kgf.

FIG. 5 shows the angle of the thigh relative to the torso of the user and the motor 8 when the program shown in FIG. 4 is executed.
It is a figure which shows the relationship with the operation state of. FIG. 5 (A) is a diagram showing the relationship between the thigh angle of the right foot with respect to the torso of the user and the operating state of the motor 8, and FIG. 5 (B) shows the thigh angle of the left foot with respect to the torso of the user. FIG. 4 is a diagram illustrating a relationship with an operation state of a motor 8. Time t1, t3, t5, t7 in the figure
At this time, a pulse having a predetermined pulse width is periodically supplied to the motor 8 (step S4 in FIG. 4), and a time t
At 2, t4, t6 and t8, the supply of the pulse to the motor 8 is stopped (step S5 in FIG. 4).

FIG. 5C is a diagram showing a state where the user is walking. The numbers 1 to 12 in FIG. 5C correspond to the numbers in the left columns 1 to 12 of Table 1 below.

In the column of thigh angle in Table 1 below, "A increase"
Indicates an increase in the A direction (the direction of rotation of the foot when the user steps on the foot), "B increase" indicates an increase in the direction of B (the direction of rotation of the foot when the user pulls the foot back), “A maximum” indicates the maximum angle in the A direction. In the column of the right motor and the left motor in Table 1, “A drive” indicates that the motor 8 is driven in the A direction.

[0023]

[Table 1]

As described above, according to the present embodiment,
Detecting the angle of the thigh with respect to the torso of the user in the front-back direction, time-differentiating the detected angle, and determining whether the detected angle is increasing in the direction in which the foot is stepped forward from the differential value. If the angle is increasing in the direction in which the foot is stepped forward, a pulse of a predetermined pulse width is periodically sent to the motor 8 in order to assist walking of the foot whose angle is increasing. Since it is supplied, it is possible to easily assist everyday walking motion.

(Second Embodiment) The configuration of a walking assist device according to a second embodiment of the present invention is the same as that of the walking assist device 100 according to the first embodiment. The description is omitted. The walking assist device according to the present embodiment is different from the walking assist device 10 in that it has an assisting function for pulling back the foot in addition to an assisting function for stepping on the foot.
Different from 0. Thereby, when climbing the stairs, it is possible to assist the operation of extending the legs to the upper stage to lift the body and the operation of extending both legs when standing up from the state of sitting on the chair.

FIG. 6 is a flowchart showing a program executed by the CPU 94. This program is executed in parallel for each of the left and right feet.

First, steps S1 and S2 in FIG.
Similarly, the angle of the thigh with respect to the torso of the user in the front-rear direction is detected (step S10), and the detected angle is differentiated with time (step S11).

Next, it is determined from the differential value whether or not the angle detected in step S10 is increasing in the direction in which both feet are stepped forward (step S12), and the angle is increased in the direction in which both feet are stepped forward. Motor 8
This program ends without being driven. This is because it is assumed that when the user sits on the chair, it is easy to sit on the chair.

If it is determined in step S12 that the angle has not increased in the direction in which both feet are stepped forward, step S1
Proceed to 3. Steps S13 and S14 are the same as steps S3 and S4 in FIG. 4 described above, and a description thereof will be omitted.

In step S14, after a pulse having a predetermined pulse width is periodically supplied to the motor 8, the program is terminated.

Next, in step S13, if the detected angle does not increase in the direction in which the foot is stepped forward, the angle detected in step S10 is changed from the differential value in step S11 to the direction in which the foot is pulled backward. It is determined whether or not the angle has increased (step S15). If the angle has increased in a direction in which the foot is pulled backward, the motor 8 is provided with a predetermined value to assist the foot with the increased angle. Is periodically supplied (step S16), and if the angle is not increasing in the direction of pulling the foot backward, the pulse is supplied to the motor 8. Then, the drive of the motor 8 is stopped (step S17), and the program ends.

The force for assisting the foot by the motor 8 is controlled so as to be smaller than the force that the user originally has to depress the foot forward and the force to pull the foot backward. In the case of assisting the stepping force, 5
The driving force of the motor 8 is controlled so as not to exceed kgf.

FIG. 7 shows the thigh angle with respect to the torso of the user and the motor 8 when the program shown in FIG. 6 is executed.
It is a figure which shows the relationship with the operation state of. FIG. 7A is a diagram showing the relationship between the thigh angle of the right foot with respect to the torso of the user and the operating state of the motor 8, and FIG. 7B is a diagram illustrating the thigh angle of the left foot with respect to the torso of the user. FIG. 4 is a diagram illustrating a relationship with an operation state of a motor 8.

Times t11, t13, t15, t1 in the figure
At times t9, t21, and t23, as described in step S14 of FIG. 6, the supply of a pulse having a predetermined pulse width to the motor 8 is started periodically, and the times t12, t14, and t12 are started.
At times t16, t18, t20, and t22, as described in step S16 of FIG. 6, the supply of the pulse having the predetermined pulse width to the motor 8 is started periodically.
At t24, the supply of the pulse to the motor 8 is stopped as described in step S17 of FIG.

FIG. 7C is a diagram showing a state where the user is walking. The numbers 1 to 17 in FIG. 7C correspond to the numbers 1 to 17 in the left column of Table 2 below.

In the column of thigh angle in Table 2 below, "A increase"
Indicates an increase in the A direction (the direction of rotation of the foot when the user steps on the foot), "B increase" indicates an increase in the direction of B (the direction of rotation of the foot when the user pulls the foot back), “A maximum” indicates the maximum angle in the A direction, and “B maximum” indicates the maximum angle in the B direction. In the right motor and left motor columns in Table 2, "A drive" indicates that the motor 8 is driven in the A direction, and "B drive" indicates that the motor 8 is driven in the B direction.

[0037]

[Table 2]

FIG. 8 shows the angle of the thigh relative to the torso of the user and the motor 8 when the program shown in FIG. 6 is executed.
It is a figure which shows the relationship with the operation state of. FIG. 8A is a diagram showing the relationship between the thigh angle of the right foot with respect to the torso of the user and the operating state of the motor 8, and FIG. 8B is a diagram illustrating the thigh angle of the left foot with respect to the torso of the user. FIG. 4 is a diagram illustrating a relationship with an operation state of a motor 8.

At time t25 in the figure, the angle of the thigh in the front-back direction with respect to the torso of the user increases in the direction in which both feet are stepped forward, so that it is easy to sit on a chair without assisting by the motor 8. (Step S1 in FIG. 6)
2 is YES). At time t26, a pulse having a predetermined pulse width is periodically supplied to the motor 8 (step S14 in FIG. 6).
Is stopped (step S in FIG. 6).
17).

FIG. 8C is a diagram showing a state where the user is seated and a state where the user stands up. The numbers 1 to 5 in FIG. 8C correspond to the numbers in the left columns 1 to 5 of Table 3 below.

In the column of the thigh angle in Table 3 below, "A increased"
Indicates an increase in the direction A (the direction of rotation of the foot when the user steps on the foot), and "B increase" indicates an increase in the direction B (the direction of rotation of the foot when the user pulls the foot back). Also,
In the column of the right motor and the left motor in Table 3, “B drive” indicates that the motor 8 is driven in the B direction.

[0042]

[Table 3]

As described above, according to the present embodiment,
The angle in the front-back direction of both thighs with respect to the torso of the user is detected, the detected angle is differentiated with respect to time, and the detected angle is increased from the differential value in the direction in which both feet are stepped forward. However, if the angle is increasing in a direction in which one foot is stepped forward or one foot is pulled backward, a pulse having a predetermined pulse width is supplied to the motor 8 in order to assist walking of the foot whose angle is increasing. Since the power is supplied periodically, it is possible to easily assist daily walking motion and leg stretching motion.

If the angle in the front-back direction of both thighs with respect to the torso of the user is increasing in the direction in which both feet are stepped forward, the present program is terminated without assisting by the motor 8. If the user sits on a chair,
It is easy to sit on a chair.

(Third Embodiment) FIG. 9 shows a third embodiment of the present invention.
It is a figure showing composition of walk auxiliary equipment 200 concerning an embodiment.

The walking assist device 200 differs from the walking assist device 100 only in that it has a pressure-sensitive sensor 19 for detecting the pressure applied to the sole of the foot, and the other configuration is the same. I do.

The pressure sensor 19 is connected to the control unit 9 and, when detecting a pressure applied to the sole, outputs a signal corresponding to the pressure to the control unit 9.

FIG. 10 is a diagram showing the configuration of the control unit 9. The control unit 9 of the present embodiment is provided with a pressure detection program 96 for detecting the pressure applied to the sole of the foot based on the signal output from the pressure-sensitive sensor 19, compared to the control unit 9 of FIG. And a setting unit 25 that allows the user to freely set parameters serving as conditions for assisting is connected, and other configurations are the same. .

The CPU 94 outputs a signal corresponding to the rotation speed of the gear 6 output from the rotation detection sensor 7 and the pressure-sensitive sensor 1
9 is input to the input / output interface 91, the angle detection program 95 and the pressure detection program 96 are executed to determine the front-back angle of the thigh with respect to the torso of the user and the pressure applied to the sole. To detect. Then, it is determined whether to drive the motor 8 based on the detected angle and pressure, and a signal corresponding to the determination result is output to the motor 8 via the input / output interface 91. The motor 8 is driven by a signal input from the CPU 94.

FIG. 11 is a flowchart showing a program executed by the CPU 94. This program is executed in parallel for each of the left and right feet.

First, a setting unit 25 sets a threshold value THθ1, a threshold value THθ2, and a pressure threshold value THP of the angle per unit time described later.
(Step S21), and the signal output from the pressure-sensitive sensor 19 is
When input to 1, the pressure detection program 96 is executed,
The pressure applied to the right and left soles is detected (step S2
2). The pressure applied to one of the soles is a threshold
It is determined whether or not the pressure is greater than THP (step S23). If the pressure applied to one of the soles is greater than the threshold value THP, it is determined that the vehicle is descending the stairs, and the motor 8 is instructed so that both feet do not assist. The supply of the pulse is stopped, and the driving of the motor 8 is stopped (step S24).

Thereafter, it is determined whether or not the pressure on the soles of both feet is smaller than a threshold value THP for a predetermined time (step S2).
5) If the pressure applied to one of the soles within the predetermined period is equal to or greater than the threshold value THP, the process returns to step S21 after waiting for the sole pressure of both feet to become smaller than the threshold value THP for the predetermined period. .

If it is determined in step S23 that the pressure applied to one of the soles is equal to or less than the threshold value THP, the flow proceeds to step S23.
Proceed to 26. Steps S26 to S33 are almost the same as steps S10 to S17 in FIG. 6 described above, and therefore only different points will be described.

The differential value in step S27 is equal to the threshold THθ1.
That is, it is determined whether or not the angle detected in step S26 is increasing in the direction in which the foot is stepped forward (step S29), and the angle is increased in the direction in which the foot is stepped forward. In this case, the process proceeds to step S30. On the other hand, if the angle does not increase in the direction in which the foot is stepped forward, it is determined whether the differential value in step S27 is equal to or greater than the threshold THθ2, that is, the angle detected in step S26 is the direction in which the foot is pulled backward. Is determined (step S31). If the angle is increasing in the direction of pulling the foot backward, the process proceeds to step S32,
If the angle has not increased in the direction in which the foot is pulled backward, the process proceeds to step S33.

FIG. 12 is a diagram showing the relationship among the pressure applied to the sole of the user, the angle of the thigh with respect to the torso of the user, and the operating state of the motor 8 when the program of FIG. 11 is executed. It is. FIG. 12A is a diagram showing the relationship between the pressure applied to the sole of the right foot of the user, the thigh angle of the right foot with respect to the torso of the user, and the operating state of the motor 8, and FIG. FIG. 6 is a diagram showing a relationship between pressure applied to the sole of the left foot of the user, the angle of the thigh of the left foot with respect to the torso of the user, and the operating state of the motor 8.

Times t30, t33, t36, t4 in the figure
When it is 0, it starts to periodically supply a pulse of a predetermined pulse width to the motor 8 as described in step S30 of FIG. 11, and at times t31, t34, t35, t37,
At times t39 and t41, supply of a pulse having a predetermined pulse width to the motor 8 is started periodically as described in step S32 of FIG. At times t32 and t38, the supply of the pulse to the motor 8 is stopped as described in step S24 of FIG.

FIG. 12C is a diagram showing a state where the user is walking. The numbers 1 to 18 in FIG. 12C correspond to the numbers 1 to 18 in the left column of Table 4 below.

In the column of thigh angle in Table 4 below, "A increase"
Indicates an increase in the A direction (the direction of rotation of the foot when the user steps on the foot), "B increase" indicates an increase in the direction of B (the direction of rotation of the foot when the user pulls the foot back), “A maximum” indicates the maximum angle in the A direction, and “B maximum” indicates the maximum angle in the B direction. In the right motor and left motor columns in Table 4, "A drive" indicates that the motor 8 is driven in the A direction, and "B drive" indicates that the motor 8 is driven in the B direction. Further, in the columns of the right sole pressure and the left sole pressure in Table 4, "P" indicates the sole pressure when the user stands upright with both feet, and "2P" indicates that the entire weight is applied to one foot. And "THP" indicates a threshold value of the sole pressure set by the user in the setting unit 25.

[0059]

[Table 4]

As described above, according to the present embodiment,
The walking assistance device 200 has a function of attaching the pressure-sensitive sensors 19 to the soles of both feet so that the assistance does not work when going down the stairs, and the angles per unit time for applying the assistance (threshold THθ1, threshold THθ2). Is provided, so that it is easy to go down the stairs and the user can freely set the feeling of wearing the walking assist device 200.

In the first to third embodiments, the walking state is determined based on the angle of the thigh relative to the torso of the user. However, the walking state is determined using contraction of the muscles of the feet or sensing from nerves. May be. Alternatively, the walking state may be determined by detecting the angle of the knee as shown in FIG.

As shown in FIG. 13, when a person is walking, the knee of the foot to be stepped on (the right knee in FIG. 13)
And the other leg (the left leg in FIG. 13) does not bend the knee as an axial leg. The angle at which the knee is bent is detected by an angle sensor 20 as shown in FIG. 13, and a signal corresponding to the angle detected by the angle sensor 20 is output to the control unit 9. Even if the control of the drive of the motor 8 described in is performed, the same effects as those of the present invention can be obtained.

In the first to third embodiments, the motor 8 is used as auxiliary power. However, the motor 8 moves according to the movement of the elastic body (spring, rubber), the prime mover, the air cylinder, and the knee. May be used, and these may be combined as appropriate to provide more delicate assistance.

[0064]

As described above in detail, according to the walking assist device of the first aspect, when the detecting means detects the movement of both feet, the power of the power means is controlled to assist the movement of both feet. Therefore, it is possible to easily assist a daily walking operation.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a walking assist device 100 according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a control unit 9 of FIG.

FIG. 3 is a diagram showing a situation when a user steps on a right foot.

FIG. 4 is a flowchart showing a program executed by a CPU 94 in FIG. 2 to operate the walking assist device 100 in FIG. 1;

5 is a diagram showing the relationship between the thigh angle of the user with respect to the torso and the operating state of the motor 8 when the program of FIG. 4 is executed.

FIG. 6 is a flowchart showing a program executed by a CPU 94 in FIG. 2;

7 is a diagram showing the relationship between the thigh angle of the user with respect to the torso and the operating state of the motor 8 when the program of FIG. 6 is being executed.

8 is a diagram showing the relationship between the thigh angle of the user with respect to the torso and the operating state of the motor 8 when the program in FIG. 6 is being executed.

FIG. 9 is a diagram showing a configuration of a walking assist device 200 according to a third embodiment of the present invention.

FIG. 10 is a diagram illustrating a configuration of a control unit 9 of FIG. 9;

11 is a flowchart showing a program executed by a CPU 94 in FIG.

12 is a diagram illustrating a relationship between a pressure applied to a sole of a user, an angle of a thigh with respect to a torso of the user, and an operation state of a motor 8 when the program in FIG. 11 is executed.

FIG. 13 is a diagram showing a configuration of an angle sensor 20 for detecting a knee angle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixture 2 Auxiliary device 3 Chain 4, 5, 6, 17, 18 Gear 7 Rotation detection sensor (detection means) 8 Motor (power means) 9 Control part (detection means, control means) 10 Battery 100, 200 Walking assistance device

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yoshihiko Wada 12 Kirihara-cho, Fujisawa-shi, Kanagawa Nippon Seiko Co., Ltd. (72) Inventor Hiroyuki Saito 12 Kirihara-cho, Fujisawa-shi, Kanagawa Nippon Seiko Co., Ltd.

Claims (1)

[Claims] 1. A power means having a power for assisting the movement of both feet of a human being, a detection means for detecting the movement of both feet, and when the movement of both feet is detected by the detection means, Control means for controlling the power of the power means so as to assist movement.