WO2015174670A1

WO2015174670A1 - Force control actuator module for a hand exoskeleton structure, and a hand exoskeleton system using same

Info

Publication number: WO2015174670A1
Application number: PCT/KR2015/004411
Authority: WO
Inventors: 배준범; 조인성
Original assignee: 국립대학법인 울산과학기술대학교 산학협력단
Priority date: 2014-05-12
Filing date: 2015-04-30
Publication date: 2015-11-19
Also published as: KR20150129921A; KR101682949B1

Abstract

The technical objective of the present invention is to provide a force control actuator module for a hand exoskeleton structure, the force control actuator module being compact so as to guarantee natural moving of a hand and at the same time being able to accurately transmit predetermined interactive force from a virtual object to a user. In order to obtain the technical objective, a force control actuator module for a hand exoskeleton system, according to the present invention, comprises: a first potentiometer for measuring the position of a finger linkage structure; a second potentiometer, for measuring the position of an actuator, equipped inside a linear motor; and a resilient member provided between the actuator and the finger linkage structure, wherein the resilient member functions as a force sensor, and the force transmitted from the actuator is measured by means of the deflection of the resilient member.

Description

Force Control Driver Module for Hand Exoskeleton Structure and Hand Exoskeleton System

The present invention relates to a force control driver module for a hand exoskeleton structure, in particular using a Series Elastic Actuator (SEA) mechanism, where the position of the finger link structure is measured by a potentiometer for the human side and the position of the actuator is a linear motor. A force control driver module for a hand exoskeleton structure, which is measured by a potentiometer embedded therein, and the transmitted force is controlled by a deflection of an elastic member such as a linear spring, thereby eliminating a separate force sensor. will be.

The exoskeleton system has been one of the areas of increasing interest for applications in rehabilitation or power increase, and active research is currently underway. Among the areas of research on exoskeleton systems, interaction with virtual objects using exoskeleton interfaces has become one of the most promising applications of exoskeleton systems. Many relevant studies attempting to achieve virtual reality, such as head mounted display (HMD) systems or tactile sensors, are also underway, which adds to the need for a hand wearable interaction system. .

Since hands are the richest source of tactile feedback, sophisticated interactions with virtual objects would be impossible without realistic force feedback to the hands. In order to develop a wearable interaction system for virtual reality, such a system must be able to accurately transfer certain interaction forces from the virtual object to the user while ensuring natural hand movements. Under this need, the present invention also began by proposing a compact driver module capable of accurately generating and controlling a predetermined force.

Small and force controllable actuator modules are essential in hand exoskeleton systems. Since the driver module largely determines the size and weight of the system and this has a great influence on the natural movements of the arms and fingers, the driver module should be as small and light as possible. In addition, when the user interacts with objects in the virtual world, the user understands the virtual environment and manipulates the objects based on the transmitted force information. Thus, force feedback from virtual objects is very important for hand exoskeleton systems. For force mode control, force sensors may be applied to the hand exoskeleton system, but conventional force sensors are very large and heavy, increasing the size and weight of the system.

Thus, the present invention is to provide a hand exoskeletal force control driver module that is compact enough to secure the natural movement of the hand and can accurately transfer a predetermined interaction force from the virtual object to the user. .

In order to achieve this technical problem, the force control driver module for a hand exoskeleton system according to the present invention comprises a first potentiometer configured to measure the position of the finger link structure; A second potentiometer configured to measure a position of the driver, the second potentiometer embedded in the driver; And an elastic member installed between the driver and the finger link structure, wherein the elastic member functions as a force sensor, and the force transmitted from the driver is measured by deflection of the elastic member. It is characterized by.

The elastic member is characterized in that the spring.

And, the spring is characterized in that it is designed based on the maximum grip force and the required actuator stroke.

Preferably, for the control of the force control driver module, the driver is selected from among the linearly movable drivers, for example, a linear motor, specifically a gear motor linearized by friction compensation. Can be.

This force control driver module may be configured to be installed per finger.

On the other hand, another hand exoskeleton system according to the present invention, the finger link structure, and

And a previously described force control driver module installed per finger to interact with the finger link structure.

According to the force control driver for hand exoskeleton structure according to the present invention, without the need for a separate force sensor, it is compact enough to ensure the natural movement of the hand and at the same time can accurately transfer a predetermined interaction force from the virtual object to the user Will create an effect.

1 is a schematic diagram of a SEA mechanism applied to the present invention,

2 is a schematic diagram of a driver module according to an embodiment of the present invention;

3 is an experimental result of the grip force (grip force),

4 is a small motor driver according to an embodiment of the present invention;

5 is an embodiment of the driver module manufactured by FIG.

6 shows friction identification,

7 is a block diagram of a control algorithm according to an embodiment of the present invention;

8 is a frequency response of a closed loop control system,

9 is a position tracking for a predetermined sinusoidal trajectory according to an embodiment of the present invention,

10 is a position tracking for any arbitrary trajectory in accordance with an embodiment of the present invention, and

11 illustrates a hand exoskeleton device having a driver module according to an embodiment of the present invention, respectively.

(Major drawing)

100 hand exoskeleton system

10 Force control driver module 11 First potentiometer for human side

12 Linear Motor (Driver) 13 Second Potentiometer (For Driver Side)

14 Elastic member (spring)

20 finger link structure

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the present specification and claims should not be construed as being limited to the common or dictionary meanings, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that it can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

In the present invention, the Series Elastic Actuator (SEA) mechanism is applied to the actuator module together with the electric motor to satisfy two requirements of compact size and force mode control. In the SEA mechanism, the transmitted force is measured by the spring deflection between the driver and the human side. The spring acts as a force sensor so that the size and weight of the driver module can be reduced. By adjusting the actuator position, the transmitted force is precisely controlled.

Series Elastic Actuator(SEA) 메커니즘Series Elastic Actuator (SEA) Mechanism

In order to apply the correct force feeling with a finger, force mode control is required, which requires real time force measurement. However, conventional force sensors are not suitable for hand exoskeleton systems because of their size and weight. Therefore, in the hand exoskeleton system according to the present invention, the SEA mechanism is basically applied for compact design and accurate force mode control.

In this mechanism, the force generated by the driver is transmitted via an elastic element, such as a spring, and the elastic element is installed between the human side and the driver. The transmitted force is controlled by the spring deformation. The SEA mechanism is as outlined in FIG. 1. The transmission force, f, is controlled by the following deformation of the spring.

Where k is a spring constant,

And

Indicates the positions of the driver and the human side, respectively. The predetermined actuator position is the human joint movement and the given predetermined force

Is determined as follows.

here,

Denotes a predetermined driver position. By controlling the motor position, a predetermined force can be generated accurately, so that the driver can interact with human motion by applying the appropriate interaction force according to Equation 1 above.

In the hand exoskeleton system according to the present invention, the SEA mechanism is applied to implement a force controllable driver module, a schematic of this driver module 10 is shown in FIG. 2.

The position of the finger linkage structure 20 (see FIG. 11) is measured by a first potentiometer 11 for the human side, the position of the driver being a second embedded in a linear motor 12 as an example thereof. It is measured by the potentiometer 13. The transmitted force is controlled by the deformation of the linear spring 14 which is one example of the elastic means.

Since the transmitted force is applied and measured using a linear spring deformation, the hand exoskeleton system 100 (see FIG. 11) does not require a separate force sensor. This mechanism results in a compact design of the driver module, and the sensitivity of the measuring force is easily controlled by the spring constant.

선형 스프링의 설계Design of Linear Springs

The linear spring plays a very important role in the force controllable actuator module according to the invention because the force is transmitted through the spring. Therefore, since the maximum force and sensitivity of the driver module are determined by the spring constant, the spring constant must be determined carefully.

The driver module must be able to generate a maximum grip force to apply any amount of interaction force from the virtual objects to the finger. The grip force was experimentally measured by a Tekscan Grip sensor (Tekscan. Grip System. 2013. http://www.tekscan.com/.) As shown in FIG. Grip force measurements were performed by 7 participants (4 men, 3 women, age 24 ± 4.3). They were asked to hold solid plastic cups of 6.4 cm diameter for 30 seconds, with each participant having five tests. Each finger average grip force was calculated for male and female participants and the experimental results are shown in FIG. 3 (b). The grip of the thumb was greatest for all participants, corresponding to about 8 N for men and about 6 N for women.

The linkage structure of the hand exoskeleton system has been designed by the inventors and the finger of such a system can be moved by a driver mounted on the back of the hand. The simulation results also showed that the finger tip can be bent up to 80 degrees and hyper-extended to 30 degrees with a driver link motion of about 25 degrees. With the exoskeleton structure and driver module shown in FIG. 2, it has been verified that a 25 degree rotational motion can be achieved by about 20 mm linear motion of the driver. Thus, a linear motor with a stroke of about 20 mm is needed, which can make up to 20 mm deformation. Considering the maximum force and deformation, the spring constant required is about 0.3 to 0.4 N / mm.

The spring constant is calculated by

Where G is the modulus of rigidity, d is the diameter of the spring wire, D is the average diameter of the spring, and n is the number of active coils. Considering the size of the link structure and the linear motor, the design variable was determined to make the spring constant 0.434 N / mm. The determined parameters for the spring design are shown in Table 1 below.

모터 드라이버의 설계Motor driver design

The motor driver for controlling the linear motor is also compact enough and must be fitted to a small driver module. The motor driver for the linear motor is designed manually as shown in FIG. Fig. 4A shows the circuit design for the driver, and Fig. 4B shows the motor driver actually manufactured. The control input to the motor driver is converted to a PWM signal and a full H bridge circuit is applied for normal / reverse motion of the electric motor. The size of the motor driver is 27 × 14 × 4 mm, which is small enough to be attached to the top of the linear motor.

구동기 모듈의 제조Manufacturing of Driver Modules

As shown in FIG. 5, the force controllable driver module has actually been manufactured. In order to meet the required force and stroke range, a linear motor with 20 mm stroke, 9 N maximum force and 25 mm / sec speed was chosen as the main driver. A linear spring designed by the variables in Table 1 was applied. Potentiometers for measuring finger motion were located on top of the driver module due to the limited space. The motor driver was attached to the top of the motor and hidden by a manufactured cover to protect the electrical wires. The structure in this embodiment is made of nylon using rapid prototyping technology, but it will be apparent to those skilled in the art that it is not necessarily limited to such materials and manufacturing techniques, so that within the same range Various alternatives are possible to achieve the action / effect of. The size of the driver module is about 18 x 77 x 36 mm and the weight is about 30 g.

구동기 모듈의 제어Control of Driver Module

Electric motors are generally used with gear reducers to adjust power or speed ranges. The gear reducer amplifies the output force, but this also increases the friction of the motor. If the gear ratio is so large that the geared motor is not back-drivable, friction must be properly compensated for natural human-robot interaction. Since friction in the motor corresponds to major nonlinearity, which hinders high control performance in position tracking, the force controllability of the actuator module of the present invention is drastically reduced without proper friction compensation.

In the driver module according to the present invention, a linear motor with a gear ratio of 30: 1 is used, and the friction of the motor cannot be ignored. In order to compensate for the friction of the motor, the friction model was experimentally identified. 6 shows experimentally secured control inputs at various speeds of the motor. Then, the friction is modeled by the following equation.

here,

Represents the speed of the driver. Each item in equation 4 represents bias, coulomb friction, and linear damping, respectively. By curve fitting, the variables in the friction model were specified as a = 0.05, b = 0.2 and c = 0.003475, respectively.

The linearized motor model by friction compensation was controlled by the PID controller. PID gains were tuned by experiment. 7 shows a control block diagram of the driver model.

The frequency response of the closed loop control system was experimentally obtained (see FIG. 8). As can be seen from the figure, the bandwidth frequency of the driver module is about 10 rad / sec. Considering the maximum speed of the linear motor, the experimental results indicate that the control algorithm guarantees the maximum performance of the motor.

The position tracking performance with the control algorithm according to the present invention has been experimentally verified. 9 shows tracking performance with a 5 Hz frequency and sinusoidal trajectory of 5 mm size. Linear motors follow a given position well without a large tracking error. To test the tracking performance for any trajectory, the predetermined trajectory was set to the potentiometer signal on the human side and moved randomly. Fig. 10 shows the results of experiments when the human side potentiometer moved arbitrarily. In any movement state, the tracking error is more irregular than in the case of a sinusoidal signal but it can be seen that the tracking error is less than 1 mm with a change of about 10 mm at a given position.

성능 검증Performance Verification

The driver module according to the invention is actually assembled to the hand exoskeleton structure. In this design, the generated force is transmitted to the finger tip through the exoskeleton finger linkage structure 20. In addition, the exoskeleton structure is configured to allow sufficient extension / flexion movement and three degrees of freedom for each finger for natural interaction with the hand. 11 shows a 3D design of the hand exoskeleton system 100 with the assembled actuator module 10. Both driver modules were fitted for the experiment.

The force control performance was experimentally verified with the actual exoskeleton structure. In this experiment, a predetermined force was set to a sinusoidal signal having a frequency of 0.5 Hz and a magnitude of 5 N. Fingers moved randomly. By using Equation 2, the predetermined motor position was calculated in real time by the predetermined force and finger position. According to the result of the force generation performance in any finger movement, it was confirmed that even under this arbitrary movement of the finger, the force is generated as desired without significant error.

As described above, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims below and equivalents thereof.

Claims

As a force control driver module 10 for a hand exoskeleton system,

A first potentiometer 11 configured to measure the position of the finger link structure 20;

A second potentiometer (13) configured to measure the position of the driver and embedded in the driver (12); And

An elastic member 14 installed between the driver and the finger link structure

It is made, including

And the elastic member functions as a force sensor, so that the force transmitted from the driver is measured by the deflection of the elastic member.
The method of claim 1,

The elastic member is a force control driver module, characterized in that the spring.
The method of claim 2,

And the spring is designed based on the maximum grip force and the required actuator stroke.
The method of claim 1,

And for the control of the force control driver module, the driver is selected from among linearly movable drivers.
The method of claim 1,

And the force control driver module is configured to be installed per finger.
As the hand exoskeleton system 100,

Finger link structure 20; And

The force control driver module 10 according to any one of claims 1 to 5 installed per finger to interact with the finger link structure.

Hand exoskeleton system comprising a.