JP7290490B2 - power assist device - Google Patents

Description

The present invention relates to a power assist device.

In recent years, the development of AAN (Assist-as-Needed) control has been advanced in the control method of the power assist device that assists the movement of the wearer. AAN control is a control technique that provides assistance only when the wearer needs assistance. That is, in AAN control, when the wearer can follow the target trajectory by himself, the degree of support is reduced, and when the error from the target trajectory (difference between the target trajectory and the actual trajectory of the wearer's body) is large, Try to increase the degree of support. Various studies have been made on control methods for such a power assist device.

Tatsuo Narikiyo, 3 others, ``AAN Control of Power Assisted Robot Using Velocity Field Control'', SICE Life Engineering Symposium 2018 Proceedings pp.85-88, 2018

The present inventors have developed a control method for an AAN control system by adaptive control using a neural network in consideration of dynamic mutual interference between the power assist device and the wearer in the power assist device. The characteristics of this control method are that (1) the target trajectory tracking accuracy and the magnitude of the force/torque support can be specified by two parameters, (2) the force/torque of the support determined by the control signal becomes excessively large, and the wearer The control signal can be limited to any range so as not to harm the

In the above control method and the control method of a general power assist device, basically, the power assist device is controlled so as to follow the target trajectory. However, in these control methods, it is difficult to imagine that the actually worn power assist device imagines a target time trajectory and performs control so as to accurately follow the time trajectory. Rather, it is considered that the robot creates an image of the target route and performs vague control along the image of the target route.

As described above, in order to achieve motion along the target path in the power assist device, it is not always necessary to follow the target time trajectory. In particular, when there is a large error between the target time trajectory and the current position, if the time trajectory is followed, an excessive input is generated, increasing the load on the wearer and the power assist device. Therefore, if there is a large error between the target's time trajectory and the current position, the movement on the trajectory is realized by executing speed control so that the target trajectory is reached at a certain speed instead of the time trajectory. It is important to. Therefore, it is considered that the power assist control is suitable for defining a velocity field toward the target path and performing control along the velocity field.

In Non-Patent Document 1, designing a velocity field in the work coordinate space according to the wearer's gait, setting the velocity at each coordinate as a target value, and supporting the wearer when following the target velocity with his own power ANN control is disclosed that reduces the speed and increases the assistance when the error from the target speed is large. On the other hand, in the ANN control described in Non-Patent Document 1, it is not possible to specify the dynamic interaction between the torque/force exerted by the wearer and the power assist device, so there remains a problem in improving the operational feeling of the power assist device. was

The present invention has been made in view of the above background, and is capable of more effectively suppressing dynamic mutual interference between the wearer and the power assist device, and more effectively maintaining the route following characteristics. An object of the present invention is to provide an assist device.

A power assist device according to the present invention comprises a closed-loop control system for controlling a control torque by an AAN control method. Divide the area into a near-path area within a distance and an outer area outside the near-path area, set a velocity field in the near-path area, and set a force field in the normal direction of the path along with the velocity field in the outer area. A velocity field and force field design mechanism, an impedance model setting mechanism that sets an impedance model for the velocity field that takes into account unknown dynamic characteristics that are dynamic mutual interference between the wearer and the power assist device, and the current based on the impedance model an adaptive control mechanism that performs impedance control on a velocity following error that is the difference between an actual velocity at a position and a target velocity at the current position, and estimates the unknown dynamic characteristic by a neural network, wherein the closed loop control system comprises: adjusting the parameters of the impedance model according to the speed following error in the path vicinity area, calculating the control torque based on the output from the adaptive control mechanism, and outputting from the closed loop control system in the outer area; and the force field to calculate the control torque.

In the power assist device, impedance control is performed with respect to the velocity following error based on the impedance model for the velocity field, and the parameters of the impedance model are adjusted according to the velocity following error in the region near the path. By doing so, it is possible to more effectively suppress dynamic mutual interference between the wearer and the power assist device. In addition, by setting the force field in the outer region, it is possible to generate a force to pull back to the target route when taking a trajectory that deviates greatly from the target route, and it is possible to maintain the route following characteristics more effectively.

According to the present invention, it is possible to provide a power assist device capable of more effectively suppressing dynamic mutual interference between the wearer and the power assist device and more effectively maintaining the route following characteristics.

1 is a schematic diagram showing a schematic configuration of a power assist device according to an embodiment; FIG. It is a schematic diagram which shows the state which the wearer wears the power assist apparatus. It is a block diagram showing the flow of sensor signals and control signals in the power assist device. 1 is a schematic diagram showing the configuration of a control system of a power assist device according to an embodiment; FIG. FIG. 4 is a schematic diagram showing an example of a velocity field/force field set in a working coordinate space; It is a schematic diagram explaining the setting of the velocity field _vd . FIG. 4 is a schematic diagram showing an example of an adjustment state of an impedance parameter _Di ; 4 is a graph showing temporal changes in the absolute value of interaction force f _ext in an experiment. 4 is a graph showing the trajectory of the steering wheel in working coordinates when the power assist device 1 is controlled in active mode. It is a graph which shows a time change of velocity and interaction force.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, a schematic configuration of a power assist device 1 according to the present embodiment will be described with reference to FIG. FIG. 1 is a schematic diagram showing a schematic configuration of a power assist device 1 according to this embodiment. FIG. 2 is a schematic diagram showing a state in which a wearer wears the power assist device 1. As shown in FIG.

The power assist device 1 includes a drive source that applies a control torque to each joint of the wearer with the joints of the wearer as a rotation axis, and an AAN control system that provides control torque so that the wearer can be assisted when necessary. and a control unit for controlling the That is, as shown in FIGS. 1 and 2, the power assist device 1 includes a foot support portion 21, a lower leg support member 22, an upper leg support member 23, an ankle joint rotation member 24, and a knee joint rotation member 25. , a hip joint rotating member 26, and a control box (I/O board) 30 as a control unit.

The foot support part 21 supports the sole. The lower leg support member 22 is a rod-shaped member that is arranged along the lower leg when worn by the wearer. The upper leg support member 23 is a rod-shaped member arranged along the upper leg.

The ankle joint rotating member 24 rotatably supports the foot support portion 21 and the lower leg support member 22, and includes an actuator 24a such as a servomotor for actively rotating and driving, and an angle sensor 24b such as a rotary encoder. , has The knee joint rotating member 25 rotatably supports the lower leg support member 22 and the upper leg support member 23, and includes an actuator 25a such as a servomotor for actively rotating and driving, and an angle sensor 25b such as a rotary encoder. and have The hip joint rotary member 26 rotatably supports the upper leg support member 23 and the waist support member 15, and includes an actuator 26a such as a servomotor for actively rotating and driving, and an angle sensor 26b such as a rotary encoder. , has Each actuator (actuator 24a, actuator 25a, actuator 26a) in the ankle joint rotating member 24, the knee joint rotating member 25, and the hip joint rotating member 26 controls each joint of the wearer with respect to each joint of the wearer as a rotation axis. It is a drive source that imparts torque.

A control box 30 as a control unit controls the control torque so that the wearer can be assisted when necessary by the AAN control system. The control box 30 detects sensor signals from each sensor (angle sensors 24b, 25b, 26b) and controls driving of each actuator (actuators 24a, 25a, 26a). The power assist device 1 may include at least one pressure sensor 35 such as a uniaxial force sensor for detecting the walking condition of the wearer on the sole of the foot support portion 21 . In addition, the power assist device 1 may include a gyro sensor 34 that measures the inclination of the wearer's torso in the vicinity of the wearer's back.

FIG. 3 is a block diagram showing the flow of sensor signals and control signals in the power assist device 1. As shown in FIG. As shown in FIG. 3, the control box 30 is preliminarily input with the trajectory of the toe coordinates of the free leg of a healthy person during walking measured by motion capture. Rotation angle sensor signals of the ankle joint rotating member 24, the knee joint rotating member 25, and the hip joint rotating member 26 are fed back to the control box 30 from the angle sensors 24b, 25b, and 26b, respectively. The control box 30 calculates a control torque for performing necessary power support using a velocity follow-up error, which will be described later, and outputs drive signals to the actuators 24a, 25a, 26a via the servo driver. , 26a. A sensor signal from the sole pressure sensor 35 is used to detect whether the foot is in contact with the floor surface.

Next, a method for controlling the power assist device 1 according to this embodiment will be described.
In designing the control system of the power assist device, it is necessary to consider dynamic mutual interference between the wearer and the power assist device as well as the stability of the control system. A mathematical model that considers the dynamic interaction between the wearer and the power assist device 1 is expressed as in Equation (1).

Regarding the sign of equation (1), q is the joint coordinate (measured value of the joint angle), and τ is the control torque (output torque). Moreover, the meaning of the parameters in the formula (1) is as follows.

Formula (1), which is a mathematical model expressed in the joint coordinate system, can be converted into a mathematical model expressed in the working coordinate system. Here, the work coordinates are coordinates in the work space of the power assist device 1 . The work coordinates are expressed as a function of the joint coordinates, as shown in Equation (2) below. Equation (3) is obtained by partially differentiating equation (2) with respect to q. In equation (3), J(q) is the Jacobian matrix.

Using the relationship of formulas (2) and (3), the formula model expressed in the joint coordinate system (1) is transformed into the following formula model expressed in the work coordinate system ( 4) is obtained. The meaning of the parameters of Equation (4), which is a mathematical model expressed in the working coordinate system, is as shown in Equation (5) below.

FIG. 4 is a schematic diagram showing the configuration of the control system of the power assist device 1 according to this embodiment. As shown in FIG. 4, the power assist device 1 has a closed loop control system that calculates the control torque τ to be output to each actuator (servo motor) by the AAN control method. A closed loop control system of the power assist device 1 is composed of a velocity field force field design mechanism, an impedance model setting mechanism, and a neural network control mechanism.

The velocity and force field design mechanism sets velocity and force fields in the working coordinate space. A specific method for setting the velocity field and force field in the work coordinate space will be described later. The impedance model setting mechanism sets an impedance model for the velocity field considering unknown dynamic characteristics, which is dynamic mutual interference between the wearer and the power assist device. Based on the impedance model, the adaptive control mechanism performs impedance control on the velocity following error, which is the difference between the actual velocity at the current position and the target velocity at the current position, and estimates unknown dynamic characteristics using a neural network.

Next, a specific method for setting the velocity field and force field in the work coordinate space by the velocity and force field design mechanism will be described. In the following description, FIG. 4 will also be referred to as appropriate.
FIG. 5 is a schematic diagram showing an example of the velocity field/force field set in the working coordinate space. As shown in FIG. 5, first, the work coordinate space is divided into a route neighborhood region R1 located at a constant distance _d0 from a target route (route indicated by a dashed line) set in the work coordinate space, and a route neighborhood region R1 is divided into an outer region R2 outside the region.

In the work coordinate space, a velocity field _vd is set in the route vicinity region R1. FIG. 6 is a schematic diagram illustrating setting of the velocity field _vd . As shown in FIG. 6, first, a point (nearest neighbor point) Q located on the parametric curve C and closest to the toe coordinates P of the leg on which the power assist device 1 is worn by the wearer is searched. . Then, a vector directed from the toe coordinate P of the leg on which the power assist device 1 of the wearer is wearing to the nearest point Q searched for is obtained. Subsequently, the tangent vector of the parametric curve C at the searched nearest neighbor point Q is obtained.

A velocity field _vd is calculated based on a vector directed from the toe coordinates P to the nearest point Q and a tangent vector of the parametric curve C at the nearest point Q. Here, the target part of the wearer's body is, for example, the toes or joints of the leg on which the power assist device 1 is worn by the wearer. The velocity field _vd is set as shown in Equation (6).

On the other hand, in FIG. 5, in the outer region R2, a force field _Fn is set in the normal direction of the target route along with the velocity field _vd . The force field _Fn is expressed as in Equation (7). In Equation (7), k _n and d _n are adjustment parameters.

Equation (8) of the target impedance model for the velocity field is obtained from Equation (4), which is the mathematical model expressed in the working coordinate system. Here, M _i and D _i are parameters of the impedance model (impedance parameters).

In the closed-loop control system shown in FIG. 4, we want to satisfy the relationship of formula (8). is realizable only if it is unknown, and is not realizable if it is unknown. Therefore, in the closed-loop control system shown in FIG. 4, an impedance model is set up that satisfies the relationship of equation (9) in which the impedance model output variable v _i is newly introduced.

By setting an intermediate variable r shown in the following equation (10) and modifying the equation (9), the following equation (11) is obtained. In equation (11), N are other unknown dynamics that cannot be physically modeled. This is called an unknown disturbance. The unknown dynamic characteristic N is represented by Equation (12).

The unknown dynamic characteristic N is estimated by a neural network as described above. In the neural network control mechanism shown in FIG. 4, by controlling the intermediate variable r shown in Equation (10) to be 0, Equation (9) is realized as a result. An estimated value of the unknown dynamic characteristic N is expressed as in Equation (13). where σ(z) is the radial basis function as the activation function.

In the closed-loop control system shown in FIG. 4, the control torque τ is represented by Equation (14). J is a Jacobian matrix, Tanh(r) is a dead zone function, and _Kr is an arbitrarily set parameter.

As shown in Equation (7), the force field _Fn becomes 0 in the route vicinity region R1 (see FIG. 5). Therefore, in the closed-loop control system shown in FIG. 4, the control torque τ of equation (14) is calculated based on the output from the adaptive control mechanism in the route vicinity region R1. On the other hand, in the closed-loop control system shown in FIG. 4, in the outer region R2 (see FIG. 5), the control torque τ of equation (14) is calculated based on the output from the adaptive control mechanism and the force field _Fn .

In the route vicinity area R1 shown in FIG. 5, the impedance parameters M _i and D _i are adjusted according to the speed following error. FIG. 7 is a schematic diagram showing an example of an adjustment state of the impedance parameter _Di. As shown in FIG. 7, D _i is set to D _M when r is less than -γ or greater than γ. D _i is set to D ₀ when r is greater than or equal to −γ and less than or equal to γ.

Next, an experiment for confirming the effect of the power assist device 1 according to this embodiment will be described. The power assist device 1 used in this experiment has a handle that acts on the wearer and has two control modes, an active mode and a passive mode. Here, the active mode is a mode in which the wearer moves the steering wheel of the power assist device 1 along the target route. The passive mode is a mode in which the power assist device 1 moves the steering wheel so that the steering wheel follows the target route.

FIG. 8 is a graph showing temporal changes in the absolute value of the interaction force f _ext in the experiment. Here, the horizontal axis is time [sec] and the vertical axis is the absolute value of interaction force f _ext [N]. In FIG. 8, the active mode is indicated by L1, the passive mode 1 by L2, and the passive mode 2 by L3. In passive mode 1, the control gain is set smaller than in passive mode 2. FIG.

As shown in FIG. 8, in the active mode, since the velocity field error is small, the target impedance is also designated as a small value. Therefore, the interaction force f _ext between the wearer and the power assist device 1 has a small value, and it can be seen that the power assist device 1 provides support according to the exerted force of the wearer. On the other hand, in passive mode 1 and passive mode 2, since the wearer is only in a state where the hand is placed on the steering wheel, the power assist device 1 has a large interaction in order to execute the exercise along the target path. It can be seen that the force f _ext moves the steering wheel. This is probably because the arm of the wearer acts as a load on the power assist device 1, resulting in an increase in f _ext .

FIG. 9 is a graph showing the trajectory of the steering wheel path in the working coordinates when the power assist device 1 is controlled in the active mode. Here, the horizontal axis is the x-coordinate [m] of the predetermined position of the steering wheel, and the vertical axis is the y-coordinate [m] of the predetermined position of the steering wheel. FIG. 10 is a graph showing temporal changes in velocity and interaction force. In the upper graph, the horizontal axis is time [sec] and the vertical axis is speed [m/s]. In the lower graph, the horizontal axis is time [sec] and the vertical axis is force [N]. The upper left graph shows the x-axis direction components of V _r and V _i , and the upper right graph shows the y-axis direction components of V _r and V _i . The lower left graph shows the x-axis component fx of the interaction force f _ext , and the upper right graph shows the y-axis component fy of the interaction force f _ext .

As shown in Figures 9 and 10, for the first 20 seconds, the wearer moves the handle to follow the target path. Therefore, the interaction force f _ext between the power assist device 1 and the wearer is relatively small. On the other hand, from 20 seconds to 40 seconds, the wearer intentionally moves the steering wheel so as to deviate from the target path. At this time, the interaction force f _ext between the power assist device 1 and the wearer becomes extremely large due to the force field, and it can be seen that the trajectory of the steering wheel is about to return to the region near the route at a certain distance from the target route. . From the above, it has been confirmed that the power assist device 1 according to the present embodiment provides appropriate support only when the wearer needs support.

It should be noted that the present invention is not limited to the above embodiments, and can be modified as appropriate without departing from the scope of the invention.

1 Power assist device 15 Waist support member 21 Leg support member 22 Lower leg support member 23 Upper leg support member 24 Ankle joint rotation members 24a, 25a, 26a Actuators 24b, 25b, 26b Angle sensor 25 Knee joint rotation member 26 Hip joint rotation member 30 Control Box 34 Gyro sensor 35 Pressure sensor

Claims (1)

A power assist device comprising a closed loop control system that controls the control torque by the AAN control method,
The closed-loop control system is
dividing a work coordinate space into a near-path area located at a certain distance from a target path set in the work coordinate space and an outer area outside the near-path area, and setting a velocity field in the near-path area; a velocity field and force field design mechanism that sets a force field in the normal direction of the route together with the velocity field in the outer region;
an impedance model setting mechanism for setting an impedance model for a velocity field in consideration of unknown dynamic characteristics, which is dynamic mutual interference between the wearer and the power assist device;
an adaptive control mechanism that performs impedance control on a speed following error, which is the difference between the actual speed at the current position and the target speed at the current position, based on the impedance model, and estimates the unknown dynamic characteristic by a neural network; including
In the closed loop control system,
adjusting the parameters of the impedance model according to the speed following error in the path vicinity area, calculating the control torque based on the output from the adaptive control mechanism;
A power assist device, wherein in the outer region, a control torque is calculated based on an output from the adaptive control mechanism and a force field.

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