KR101750944B1

KR101750944B1 - Slip control method for electric wheelchairs

Info

Publication number: KR101750944B1
Application number: KR1020150190963A
Authority: KR
Inventors: 이응혁; 이원영; 엄수홍; 장문석; 김보민
Original assignee: 한국산업기술대학교산학협력단
Priority date: 2014-12-31
Filing date: 2015-12-31
Publication date: 2017-06-28
Also published as: KR20160081853A

Abstract

The slip ratio is calculated using information of an encoder that reads information of a motor that drives a rear wheel in an electric wheelchair and information calculated by the inertia sensor and feeds a slip correction torque The present invention relates to a slip control apparatus and method for an electric wheelchair in which slip can be minimized by performing feed-forward control. An information detector for acquiring information of a motor driving a rear wheel of an electric wheelchair and actual speed information of the electric wheelchair; A slip rate calculator for calculating a slip rate based on information of a motor and information of an electric wheelchair; A motor speed calculator for calculating a motor speed based on input user information; A slip controller for calculating a slip correction torque for controlling the slip based on the slip ratio; A target speed compensator for calculating a slip compensation torque and a motor target speed to correct a target speed according to a slip ratio; And a motor speed controller for PID-controlling the motor by combining the target speed and feedback information of the motor, thereby realizing an electric wheelchair slip control device.

Description

[0001] Slip control method for electric wheelchairs [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slip control of an electric wheelchair, and more particularly, to a slip control of an electric wheelchair in which a left wheel motor speed and a rotational angular speed are controlled using encoder information for reading information of a motor driving a rear wheel in an electric wheelchair And the slip ratio is calculated by using the X-axis acceleration information and the YAW information calculated by the inertia sensor, and the slip correction torque based on the slip ratio is used to calculate the feed-forward torque before the final output of the left and right electric motors, The present invention relates to a slip control method for an electric wheelchair,

The aging of the elderly is one of the biggest social problems in the world. In Korea, aging is also a serious problem. In general, aged society accounts for between 7% and 14% of the population, aged society accounts for 14% to 20%, and super-aged society accounts for over 20% Classify. According to the future statistics of the Korea National Statistical Office, Korea has already entered an aging society in 2000, and it is expected to reach an aged society in 2018 and a super aged society in 2026.

As we enter the aging society, the demand for elderly goods, which are mainly used by the elderly, has started to increase. Demand for mobile aids to help older people, one of the elderly goods, is also increasing. A mobile assistive device is a device that helps the elderly to move people who are unable to move self-aged due to aging physical function. Typical examples are wheelchairs, walkers, and electric scooters. Dual wheelchairs have the highest penetration rate.

Wheelchairs have a long history that began in the 1800s as one of the mobility aids for burning people with mobility. Manual wheelchairs of the type that have to be moved by the power of a person can not travel long distances because they have to be moved uphill and downhill as well as manually on the flat ground. To overcome this, electric wheelchairs were created in 1950. An electric wheelchair is a wheelchair that rolls wheels using the power of a motor in a passive wheelchair that rolls the wheel by hand. It has evolved from manual to electric wheelchairs so that you can go uphill and downhill comfortably and comfortably at high speeds on the ground.

The possibility of safety accidents is increasing when elderly people use mobile assistive devices including such electric wheelchairs. According to the safety accident environment survey of mobile assistive devices, according to the survey of safety accident environment for migratory aids for elderly people (2013), 70 accidents occurred on slopes, followed by 36 accidents on slippery terrain, And 32 accidents.

Studies are being actively researched to prevent accidents that occur in the ramp of mobile ancillary equipment. However, it can be concluded that the accidents caused by the ground friction occurring on the ramp are more frequent than the incidents occurring on the ramp when the accidents involving slippery terrain or rough terrain are combined. However, there is almost no research in Korea to overcome the possibility of rollover in a slippery environment based on a mobile auxiliary device. Similar research has been conducted on mobile platforms, that is, technologies for responding to slippery terrain or rough terrain in automotive environments.

In order to control the slip during running using a small SUGV platform, a study on the overcoming of slip by Kim Sung Hwan disclosed in the following Non-Patent Document 1 uses the acceleration calculated not by the inertia sensor acceleration information but by using the slip ratio And to correct the slip during straight running. However, this study did not calculate the slip rate of the slip generated when the tool was turned and did not control the swing motion.

Another research is the study of Choi Hyun-doo's traveling robot disclosed in the following Non-Patent Document 2. The angular velocity is calculated through the kinematic analysis of the encoder information and mechanism mounted on the tool wheel. The slip rate is calculated by detecting the change of each calculated road surface of the acceleration. This study is an algorithm that can not be used without a complete kinematic analysis of the instrument to which the algorithm applies. This is an algorithm that can not be applied in general.

In addition, Park Jong-Hyun's research disclosed in the following Non-Patent Document 3 is a study based on a vehicle platform. As an in-depth study on a TCS (Traction Control System) algorithm of an automobile platform. The optimum slip ratio is calculated and calculated mechanically with respect to the slip phenomenon occurring when the vehicle is turning, so that the slip ratio generated when the vehicle turns is appropriately determined by using the engine and the brake so that the vehicle can converge at the time of turning. The slip rate was maintained. However, this study is not only different from electric wheelchair, but also has a slip control that occurs during turning, and a slip rate calculation for slip control.

Also, in the following Non-Patent Document 4, Oscar chuy, a precedent research example of the overseas study, has studied the slip control of a wheelchair. The purpose of this study was to investigate the control of slip phenomenon in wheelchair using electric wheelchair. This study was based on a six - wheeled wheelchair platform. The maximum traction value of the electric wheelchair was obtained and the slip phenomenon was controlled by limiting the traction value. However, the computation device of the electric wheelchair which was tested did not use the control using the conventional microcontroller, but operated by the personal computer. In this study, the sensor value measured in the electric wheelchair was computed by the computer and finally the target slip rate and the target speed of the motor were calculated and applied to the motor drive of the electric wheelchair to control the electric wheelchair.

In the embedded system, which is a typical electric wheelchair control system, there is a physical volume difference, but the calculation algorithm of the control algorithm is large.

In this study, the electric wheelchair was controlled by calculating only the slip. The case of slip occurring during turning is not considered in this study.

Kim, Sung Hwan, "A Method for Preventing Slip and Rollover of Small SUGV Using Accelerometer 2 DOF Mission Equipment", Proceedings of the Korean Society of Precision Engineering Fall Conference, pp. 187-188, 2011 Choi, Hyun-Do, "Traction Control of Traveling Robot Based on Slip Detected by Angular Velocity Change", Journal of Control, Robot System and Systems, Vol. 15, No. 2, pp. 184-191, 2009.2 Park, JH, "Optimal Driving Wheel Slip Control for Driving Safety of Vehicles at Turning", Korea Society of Automotive Engineers, Vol. 5, No. 4, pp. 190-198, 1997 Chuy O, "Slip mitigation control for an electric porwerd wheelchiar" Robotics and Automation (ICRA), 2014 IEEE International Conference on, pp. 333-338, 2014

However, the conventional technique does not calculate the slip rate of the slip generated when the apparatus is turned, and it is impossible to control the swing motion.

In addition, the prior art can not be used without a complete kinematic analysis of the mechanism to which the algorithm is applied, which is a disadvantage that it can not be universally applied.

In addition, Park Jong - hyun 's research has a disadvantage in that it is not only an electric wheelchair but also a platform that is different from that of an electric wheelchair.

In addition, the prior art of the overseas research example has a disadvantage that it can not be regarded as a complete slip control because the electric wheelchair is controlled by calculating only the slip slip, and the case of slip occurring in the swing traveling is not considered.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above problems occurring in the prior art, and it is an object of the present invention to provide an electric wheelchair which is capable of detecting an in- The slip ratio is calculated using the X-axis acceleration information and the YAW information calculated by the inertia sensor, and the final output of the left and right electric motors is calculated using the slip correction torque calculated based on the slip ratio And an object of the present invention is to provide a slip control method of an electric wheelchair in which feed-forward control is performed before slip is minimized.

It is another object of the present invention to provide a slip control method of a motorized chlele at which a traveling close to a designated route is guided during a small road running, thereby minimizing the risk of path deviation and overturning due to slipping.

According to an aspect of the present invention, there is provided a slip control apparatus for an electric wheelchair comprising: a user input device for receiving operation information of a user; An information detector for acquiring information of a motor driving a rear wheel of an electric wheelchair and actual speed information of the electric wheelchair; A slip rate calculator for calculating a slip rate based on the information of the motor and the information of the electric wheel chair acquired by the information detector; A motor speed calculator for calculating a motor speed based on user information inputted through the user input device; A slip controller for calculating a slip correction torque for controlling the slip based on the slip ratio calculated by the slip ratio calculator; A target speed corrector for calculating a slip correction torque calculated by the slip controller and a motor target speed calculated by the motor speed calculator to correct a target speed according to a slip ratio; And a motor speed controller for PID-controlling the motor by combining the target speed outputted from the target speed corrector and feedback information of the motor.

Wherein the information detector comprises: a first encoder for obtaining information of a motor for rotating the right rear wheel; A second encoder for acquiring information of a motor for rotating the left rear wheel; And an inertial sensor for acquiring velocity and acceleration information of the electric wheelchair.

Wherein the slip rate calculator includes an acceleration calculator for calculating an acceleration of the entire motor on the basis of the velocities of the left and right motors respectively obtained by the first and second encoders; And a slip ratio calculating unit for calculating a slip ratio by comparing the acceleration of the motor calculated by the acceleration calculator with the acceleration of the electric wheel chair acquired by the inertial sensor.

The slip rate calculator includes an angular velocity calculator for calculating an angular velocity from the speed information of the motor by the first encoder; A slip speed calculator for calculating the speed of the entire motor based on the motor speed information of the first encoder and the speed information of the second encoder; A turning slip ratio calculator for calculating a turning slip ratio based on the speed information calculated by the angular speed calculator and the YAW axis information obtained by the inertia sensor; A slip ratio calculating unit for calculating a slip ratio by comparing the acceleration of the motor calculated by the slip speed calculator and the acceleration of the electric wheel chair acquired by the inertial sensor; And a final slip ratio calculator for calculating a slip ratio calculated by the slip ratio calculating unit and a turning slip ratio calculated by the swing slip ratio calculating unit to output a final slip ratio.

Wherein the slip controller comprises: a slip detector for detecting the slip based on the slip ratio calculated by the slip ratio calculator; And a speed converter for correcting the target speed based on the slip ratio detected by the slip detector.

According to another aspect of the present invention, there is provided a sleep control method for an electric wheelchair comprising the steps of: (a) acquiring information on a motor for driving a rear wheel of an electric wheelchair and actual speed information of the electric wheelchair; (b) calculating a slip ratio based on the obtained information of the motor and the information of the electric wheel chair; (c) calculating a slip correction torque for controlling the slip based on the calculated slip ratio, and combining the slip correction torque and the target speed calculated according to the slip ratio to prevent slip by PID control of the motor .

The step (b) includes the steps of: (b1) calculating a slip ratio during a straight running based on the obtained information of the motor and the information of the electric wheel chair; (b2) calculating a slip ratio when turning on the basis of the obtained information of the motor and the information of the electric wheel chair; (b3) calculating the total slip ratio by combining the calculated slip ratio during straight running and the slip ratio during the turning running.

Wherein the step (c) includes: (c1) obtaining a final slip ratio; (c2) calculating a slip correction torque based on the obtained slip ratio, and calculating a motor control speed based on the calculated slip correction torque; (c3) driving the motor by PID control based on the calculated motor control speed.

(C2) calculating the motor control speed by adding the slip correction torque (correction value) to the target speed if the slip ratio is less than the first set value; (c22) calculating the motor control speed by subtracting the slip correction torque (correction value) from the target speed if the slip ratio is equal to or greater than the second set value; (c23) setting the motor control speed to the target speed if the slip ratio is equal to or greater than the first set value and less than the second set value.

According to the present invention, the left and right motor speeds and rotational angular velocities are extracted using encoder information for reading information of a motor that drives a rear wheel in an electric wheelchair, and the X-axis acceleration The slip ratio is calculated using information and YAW information, and feed-forward control is performed before the final output of the left and right electric motors by using the slip correction torque calculated based on the slip ratio, thereby minimizing the slip .

In addition, according to the present invention, it is possible to minimize the risk of deviation or overturning due to slipping by inducing a running close to a designated route when traveling on a small road surface.

1 is a configuration diagram of a slip control apparatus for an electric wheelchair according to the present invention,
Fig. 2 is an exemplary configuration of a slip,
3 is a diagram showing the configuration of the first embodiment of the slip rate calculator of FIG. 1,
4 is a block diagram of an embodiment of a slip rate calculator in a turning path,
5 is a configuration diagram of an electric wheelchair to which the present invention is applied;
6 is a motor and gearbox configuration diagram,
8 is a graph showing a relationship between a friction coefficient and a slip ratio,
Figure 9 also shows the relationship between speed and torque,
10 is a block diagram of an embodiment of a sleep controller,
11 is a block diagram of a general PID controller,
FIG. 12 and FIG. 13 are flowcharts showing a method of controlling a slip of an electric wheelchair according to the present invention,
14 is a magnified photograph of the electric wheel chair used in the experiment,
15 is a configuration diagram of an electric wheel chair used in the experiment of the present invention,
16 is a system block diagram of an electric wheelchair,
17 is a view showing an example of sensor information display according to the inertial sensor arrangement provided in the electric wheel chair,
Fig. 18 is a schematic diagram of the proposed route,
FIG. 19 is a diagram of an actually manufactured path,
20 is an illustration of an experimental scene of a slip rate calculator,
21 is an example of an acceleration calculated by the encoder, the inertial sensor,
Fig. 22 is an example of the rotational angular velocity calculated by the encoder and the inertial sensor,
23 is a graph showing slip ratio graphs in the straight section,
24 is a graph showing a slip ratio graph in the turning section,
25 shows the slip rate graph in the composite path,
FIG. 26 is an exemplary travel path information of a straight section in a wet state in a sleep controller off state,
FIG. 27 is an exemplary view showing travel route information of a straight section in a wet state in a sleep controller ON state,
Fig. 28 is an exemplary view of compound path driving information in a wet state in the sleep controller off state,
FIG. 29 is an exemplary view of compound path travel information in a wet state in a sleep controller ON state; FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a slip control apparatus for an electric wheelchair according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of a slip control apparatus for an electric wheelchair according to a preferred embodiment of the present invention.

The slip control apparatus for an electric wheelchair according to the present invention includes a user input device 10, an information detector 20, a motor speed calculator 30, a slip ratio calculator 40, a slip controller 50, (60), a motor speed controller (70), and a motor (80).

The user input device 10 serves to receive user's operation information and generally means an input device such as a joystick provided on an electric wheelchair.

The information detector 20 serves to obtain information on the motor driving the rear wheel of the electric wheel chair and the actual speed information of the electric wheel chair.

The motor speed calculator 30 calculates the motor target speeds Wdes_L and Wdes_R based on the user information Vuser and Wuser inputted through the user input device 10. [

The slip rate calculator 40 calculates the slip rate based on the information of the motor acquired by the information detector 20 and the information of the electric wheel chair.

The slip controller 50 calculates the slip compensation torque for controlling the slip based on the slip ratio calculated by the slip ratio calculator 40. [

The target speed corrector 60 calculates the slip correction torque calculated by the slip controller 50 and the motor target speed calculated by the motor speed calculator 30 to correct the target speed according to the slip ratio.

The motor speed controller 70 performs PID control of the motor by combining the target speed outputted from the target speed corrector 60 and feedback information of the motor.

The motor 80 is an electric motor that rotates the rear wheel of the electric wheel chair, and is roughly divided into a left motor and a right motor.

The operation of the slip controller of the electric wheelchair according to the present invention will be described in detail with reference to the accompanying drawings.

First, a user using an electric wheelchair inputs direction and speed through a user input device 10 such as a joystick.

The right rear wheel and the left rear wheel are rotated by the motor 80 that rotates the rear wheel of the initial electric wheel chair according to the direction and the speed to move the electric wheel chair.

When the movement of the electric wheelchair is started, the information detector 20 detects various information for the slip control. For example, the information of the left and right rear wheels is acquired through the first and second encoders, and the information of the electric wheel chair is detected using the inertial sensor. Here, velocity and acceleration information of the left and right motors can be detected through the first and second encoders, and X-axis acceleration information and YAW information can be detected through the inertial sensor.

The motor speed calculator 30 calculates a target speed for driving the motor 80 based on the speed information input by the user. Here, the target speed of the motor is roughly divided into a left target speed Wdes_L and a right target speed Wdes_R.

Next, the slip rate calculator 40 calculates the slip ratio that occurs when the electric wheelchair is traveling, in order to overcome the slip phenomenon depending on the road surface characteristics of the slippery terrain.

Here, in order to calculate the slip rate, the slip ratio is calculated using the acceleration of the electric wheelchair and the acceleration of the inertial sensor, which are calculated by the first and second encoders in the linear path, and the slip ratio is calculated through the first and second encoders The slip ratio is calculated using the rotational angular velocity of the electric wheelchair calculated using the velocity information and the rotational angular velocity calculated based on the information of the inertial sensor. The slip ratio of the complex path is calculated by synthesizing the slip ratio of the two cases.

The slip rate calculation will be described in detail as follows.

A slip is a phenomenon in which the wheel and the floor do not touch each other and the wheel slips on the ground because the frictional force between the ground and the mechanism falls. The causes of slip vary. Typically, it occurs noticeably in snowy and rainy slippery terrain, but slip phenomenon occurs due to difference of ground friction and wheel friction even in general indoor flat environment.

Electric wheelchairs are one of the primary means of transportation for patients and elderly people who can not move their body by themselves. If an accident occurs during the operation of an electric wheelchair, the electric wheelchair does not have a device to cope with the accident, and most of the users do not have protective equipment, which can cause a serious accident. To cope with this problem, it is necessary to cope with an accident that an electric wheelchair can take. One of them is coping with an accident caused by slip phenomenon.

Fig. 2 shows the configuration of the slip. The configuration of the slip is the speed (Vv) of the mechanism and the speed (Vw) of the wheel.

The conventional slip ratio is calculated through the following equation (1).

Equation (1) is a formula for calculating the slip rate of the mobile platform by calculating the slip rate of the mobile platform by comparing the speed of the mechanism with the speed of the wheel.

Conventional motor control (electric wheelchair control) uses the joystick interface information of the electric wheelchair to grasp the direction and speed desired by the user, and then sets the target speed for the input of the left and right electric motors to control the electric motor using the PID control.

Since such a general motor control method does not consider a slip, an accident caused by slip can not be prevented in advance.

In order to solve the disadvantages of the conventional motor control method as described above, a slip rate calculator is added to compare the speed of the electric wheelchair with the speed of the wheel so that the slip can be observed.

For example, the slip rate calculator 40 calculates the slip rate because it is used as a control index of the slip controller 50 for controlling the slip phenomenon. Therefore, the present invention proposes a sleep rate calculator that is applicable to an embedded system because of a small amount of calculation.

Electric wheelchairs do not always run straight or turn. Electric wheelchairs are inevitably complex. Therefore, it is necessary to calculate the slip ratio in a complex section. Analysis of multiple sections can be divided into straight section and turning section. Accordingly, the present invention proposes a slip rate calculation method in a straight section and a slip rate calculation method in a turn section. In order to calculate the slip ratio in the multiple section, it is necessary to combine the straight line and the turning slip ratio.

The slip ratio in the straight ahead section is generally expressed in terms of the speed in units of the speed of the electric wheelchair itself

And the speed of the wheel is compared to detect the slip phenomenon. However, in order to simplify the calculation amount, the slip ratio is calculated by comparing the acceleration units instead of the speed unit. This method can reduce the computational complexity and reduce the integration error that occurs during the conversion of inertial sensor information to velocity. The slip ratio in the straight section is calculated.

The slip ratio is calculated by comparing the pulse information of the encoder mounted on the rear side of the motor of the electric wheelchair with the X-axis acceleration information of the acceleration sensor information of the inertia sensor. The configuration of the slip ratio calculator at the time of going straight is shown in FIG.

To measure the slip rate of the straight section, the speed of the wheel and the speed of the electric wheelchair are required.

To this end, the information detector 20 includes a first encoder 21 for obtaining information of a motor for rotating the right rear wheel; A second encoder (22) for acquiring information of a motor for rotating the left rear wheel; And an inertial sensor 23 for obtaining velocity and acceleration information of the electric wheelchair to obtain basic information for slip rate detection.

Next, the slip rate calculator 40 includes an acceleration calculator 41 for calculating an acceleration of the entire motor based on the velocities of the left and right motors respectively obtained by the first and second encoders 21 and 22; By using the slip rate calculating unit 42 for calculating the slip ratio by comparing the acceleration of the motor calculated by the acceleration calculator 41 with the acceleration of the electric wheel chair obtained by the inertial sensor 23, The slip ratio is calculated.

For example, the speed of the electric wheelchair compares the acceleration X-axis information of the inertia sensor 23 to calculate the slip rate. To calculate the slip rate, you first need an electric wheelchair wheel speed. The formula for calculating the electric wheelchair wheel speed is shown in Equation (2) below.

Where V _R is the right motor speed, E _{R_Pulse} is the right encoder pulse, E _Resolution G is the gear ratio of the gearbox, W _wheel is the wheel circumference, T is the unit conversion constant, and S is the unit conversion constant.

Equation (2) divides the measured encoder measurement pulses by the encoder resolution and calculates the number of times the motor has returned. Then calculate the number of turns of the wheels divided by the gearbox gear ratio. Next, the speed of the right wheel is calculated by calculating a constant that changes the time, which is a variable for multiplying the circumference of the wheel and converting it into km / h, from ms to h and a constant S that changes the unit of speed from cm to km.

The following equation (3) is a formula for calculating the overall speed based on the left and right wheel speed information obtained from the above equation (2).

Wherein Vrobot the wheel speed, V _R is the right wheel velocity, V _L denotes the left road wheel speed.

For example, the left and right wheel speeds are averaged to calculate the overall speed.

Next, the slip ratio is obtained by comparing the acceleration of the wheel of the electric wheelchair with the acceleration of the inertial sensor. The following [Equation 4] is an equation for calculating the acceleration.

Where A _W is the acceleration of the wheel, S _cycle is the system period, and V _robot _-n-1 (V _v _- ₁ ) is the previous velocity.

For example, based on the speed of the wheel, the acceleration can be calculated by dividing by the system cycle using the previous speed difference. The X-axis acceleration value of the calculated electric wheelchair is compared with the acceleration value of the calculated wheel to calculate the slip rate in the straight path. The equation for calculating the slip rate in the straight path is shown in Equation (5) below.

Here, λ _ST represents the linear slip ratio.

For example, the straight slip ratio is calculated using the electric wheelchair speed (A _IMU ) and the electric wheelchair wheel speed (A _W ).

The slip ratio calculation method in the general turning section compares the lateral force calculated from the lateral force of the moving platform and the output power of the motor to calculate the slip ratio. The slip rate calculation method in the turning section proposed in the present invention is as follows. If the speed difference between the left and right wheels occurs, the YAW axis rotation occurs due to this difference. This is expressed as a rotation angular velocity. The slip ratio is calculated by comparing the rotational angular velocity of the electric wheelchair wheel based on the YAW axis information of the gyro sensor and the encoder information. This is a slip rate calculation algorithm in the turnaround section, which can reduce the error and reduce the error by reducing the calculation steps like the slip rate calculation in the straight line section.

4 is a block diagram of the slip ratio calculator in the turning path.

The slip rate calculator (40) includes an angular velocity calculator (43) for calculating an angular velocity from the speed information of the motor by the first encoder (21); A slip speed calculator (44) for calculating a speed of the entire motor based on the motor speed information of the first encoder (21) and the speed information of the second encoder (22); A turning slip ratio calculator 45 for calculating a turning slip ratio based on the speed information calculated by the angular speed calculator 43 and the YAW shaft information obtained by the inertia sensor 23; A slip ratio calculating unit 46 for calculating a slip ratio by comparing the acceleration of the motor calculated by the slip speed calculator 44 with the acceleration of the electric wheel chair acquired by the inertial sensor 23; And a final slip ratio calculator 47 for calculating a slip ratio calculated by the slip ratio calculator 46 and a swing slip ratio calculated by the swing slip ratio calculator 45 to output a final slip ratio.

In order to calculate the rotational angular velocity of the slip ratio calculator 40 at the time of turning, the velocity information of the left and right wheels is first required. The equation for calculating the velocities of the left and right wheels is shown in Equation (2). If the velocity information of the left and right wheels is known, it is possible to calculate the turning angular velocity based on this information. The turning angular velocity calculating equation is as shown in Equation (5).

In Equation (6), the rotational angular velocity is calculated by dividing the wheel-to-wheel distance based on the information of the left and right velocities of the wheel. The angular conversion constant is calculated for the calculated rotational angular velocity to calculate the rotational angular velocity of the final wheel.

Where T _D is the angle conversion constant, and L _Track is the distance between the axes of the wheels.

The slip rate is calculated using the following equation (7) by comparing the rotational angular velocity of the calculated wheel with the rotational angular velocity of the electric wheelchair.

Here YAW _IMU Represents the rotational angular velocity of the wheelchair.

Next, the slip rate calculator 40 in the complex path calculates the slip rate in the entire path by summing the slip rate in the straight section and the slip rate in the turn section. The slip rate summation criterion can distinguish the straightness and the turning based on the acceleration X axis information and the gyro YAW axis information. However, in the present invention, not the inertia sensor information, but the slip ratio in the complex path is calculated by adding a larger part of the slip ratio in the calculated straight line and swivel path to the final slip ratio. The configuration of the sleep rate calculator in the complex path is shown in FIG.

For example, the velocity of the left and right wheels is calculated based on the encoder information, and the slip ratio of the linear path calculated by comparing two pieces of information obtained by converting the acceleration X axis information to velocity is calculated. Then, based on the encoder information, the left and right velocities of the wheels are calculated, and the rotation acceleration is calculated based on the information to calculate the slip ratio in the turning path by comparing with the gyro YAW axis information. And the final slip ratio in the composite path is calculated by adding the slip ratio to the larger slip ratio. The formula for calculating the final slip rate is shown in Equation (8) below.

Where λ _ALL represents the final slip rate.

Equation (8) calculates the final slip ratio by applying the slip ratio of the straight path to the final slip rate, [lambda] _ALL , when the straight path slip rate [lambda] _ST is greater than the slew rate slip rate [lambda] _RO . The calculated final slip ratio is used as a control variable of the slip controller 50 described later.

Next, the slip controller 50 controls the slip phenomenon through speed control in order to maintain an appropriate slip ratio of the electric wheel chair. Slip phenomenon is a phenomenon that occurs mainly in slippery terrain. However, the slip phenomenon occurs not only in slippery areas but also in general terrain. When the slip phenomenon occurs weakly, path deviation such as understeer or oversteer [12] occurs as shown in Fig.

In the case of slip occurrence, the output power of the motor is not effectively transmitted through the wheel during the operation of the electric wheelchair, resulting in an inefficient running. In addition, if a slip phenomenon occurs strongly when operating an electric wheelchair, dangerous accidents such as rollover accidents may occur. Most elderly people or patients who use electric wheelchairs without protective equipment can lead to a greater accident than the average person because there is no immediate way to cope.

To prevent accidents caused by this slip, control the slip phenomenon

Needs to be. In order to control the slip phenomenon, it is necessary to know the slip rate which is an index of the slip phenomenon. The definition and calculation of the slip rate have already been confirmed by the slip calculator 40. In order to effectively control the slip phenomenon based on the calculated slip ratio, it is necessary to calculate an appropriate slip ratio in the slip phenomenon.

8 is a graph showing slip ratios and frictional coefficients of the driving force (Tractive Force) and the lateral force (Lateral Force). The traction control area shown in the graph is an area where the traction force and the lateral force can operate efficiently at the same time. The range is 10% to 30%.

9 is a graph showing a correlation between the speed of the electric motor and the torque. The torque can also be adjusted through the speed control to reach the optimum slip rate. Generally, the output range of the motor is 0% ~ 80%. The reason is to have stable margin. According to the graph above, the maximum torque is obtained when the motor output is 80%. If you look at the path from 0% to 80%, it can be said that the torque also increases with the speed.

Therefore, in the present invention, to alleviate the slip phenomenon occurring in the sliding terrain,

A slip controller is proposed. The slip controller controls the output speed through the slip controller 50 to maintain the slip ratio within the range of 10% to 30%, thereby adjusting the torque to alleviate the slip phenomenon.

The slip controller 50 performs a slip control by adding a correction value (slip correction torque) to the target speed when the slip ratio is less than 10% based on the slip ratio calculated by the slip ratio detector 40. When the slip ratio is 30 %, The slip control is performed by sensing the correction value at the target speed. When converging into the rated slip ratio of 10% to 30%, the target speed is directly applied to the motor speed controller 70 without adding or subtracting the correction value. To this end, the slip controller 50 calculates and outputs the slip compensation torque according to the slip ratio, and the target speed compensator 60 calculates the slip compensation torque and the target speed output from the motor speed calculator 30 And transmits the final target speed value to the motor speed controller 70. The motor speed controller 70 is finally applied to the left and right electric motor 80 using the PID control method to output the target speed.

FIG. 10 is a block diagram of the sleep controller 50. FIG. And the slip rate detected by the slip rate calculator 40 is detected by the slip detector 51. [ Then, when the slip phenomenon is detected in the speed converter 52, the target speed is corrected based on the calculated slip ratio. The correction speed is calculated through the following equation (9). Here, the slip phenomenon occurs when the motor is idling.

TS is the correction target velocity, V _Robot (Electric wheelchair), and TV _gain is the target speed gain.

The target speed gain is calculated at the target speed according to the final slip ratio, and the correction target speed is calculated to be combined with the final target speed.

The PID controller is one of the universal motor control methods generally used in the field. The PID controller basically has the form of a feedback controller and measures the output value of the object to be controlled and compares it with a reference value or a setpoint to be desired, ), And calculates the control value required for the control by using the error value. The standard type PID controller is configured to compute the manipulated variable (MV) by adding three terms as shown in the following equation.

These terms are named Proportional.Integral.Derivative controller because they are proportional to the error value, the integral of the error value, and the derivative of the error value, respectively. The intuitive meaning of these three terms is as follows.

Proportional term: Control function proportional to the magnitude of the error value in the current state.

Integral term: acts to eliminate steady-state errors.

Derivative: Brakes on sudden changes in output value to reduce overshoot and improve stability.

11 is a configuration diagram of a general PID controller. The PID controller is used in the form of the above standard, but in some cases it is used in a slightly modified form. For example, the controller may have a proportional port, or may be simplified in the form of a controller having only a proportional-integral and a proportional-differential port, which are called P, PI, and PD controllers, respectively.

In the present invention, this PID controller is used and a torque PID controller is used in the PID controller. There are two types of PID controllers: speed PID controller and torque PID controller. Among them, the torque PID that can indirectly calculate the frictional force with the ground was used. Torque that can control the motor PID controller uses torque PID controller which can use the weighting unit more effectively than the speed unit.

Here, a gain is a control parameter, which is called a gain value or gain. The process of calculating the appropriate gain value through mathematical or experimental / empirical methods is called tuning. There are many ways to adjust the gain of a PID controller, the most famous of which is the Ziegler-Nicholas method of mathematical methods.

However, in the present invention, by using the matlab pid tune function of mathwork,

The gain was tuned by adjusting the target arrival time of the PID controller used in the invention, and the tuning was performed once again by adjusting the bandwidth and phase margin.

12 and 13 are flowcharts showing a method of controlling the slip of an electric wheelchair according to the present invention.

12 and 13, (a) steps (S101 to S103) of receiving information on a motor that receives user's operation information and drives a rear wheel of the electric wheelchair and actual speed information of the electric wheelchair; (b) calculating a slip ratio based on the obtained motor information and the information of the electric wheel chair (S104 to S107); (c) calculating a slip correction torque for controlling the slip based on the calculated slip ratio, combining the slip correction torque calculated according to the slip ratio and the target speed to prevent the slip by PID control of the motor (S201 To S208).

The step (b) includes the steps of: (b1) calculating slip ratios (S102, S104) during straight traveling based on the obtained motor information and the information of the electric wheel chair; (b2) calculating slip ratios (S103, S105) when turning on the basis of the information of the obtained motor and the information of the electric wheel chair; (b3) calculating the total slip ratio by combining the calculated slip ratio during the straight running and the slip ratio during the turning running (S106, S107).

The step (c) includes the steps of: (c1) obtaining a final slip ratio (S201); (c2) calculating a slip correction torque based on the obtained slip ratio, and calculating a motor control speed based on the calculated slip correction torque (S202 to S206); (c3) driving the motor by PID control based on the calculated motor control speed (S207 to S208).

(C2) calculating (S202, S204) the motor control speed by adding the slip correction torque (correction value) to the target speed if the slip ratio is less than the first set value (10%); (c22) calculating a motor control speed by subtracting the slip compensation torque (correction value) from the target speed if the slip ratio is equal to or greater than the second set value (30%) (S206); (c23) setting the motor control speed to the target speed when the slip ratio is equal to or greater than the first set value (10%) and less than the second set value (30%) (S203, S205).

12 and 13 are the same as those of the slip control apparatus for an electric wheelchair according to the present invention.

Finally, we checked the bode diagram and confirmed by simulation that the system is stable.

The gain of the PID controller is set to 0.01, I-gain = 0.005, and d-gain = 0.001 for the final PID controller. .

The electric wheelchair system used in the present invention was an electric wheelchair for mass production made by Chungwoo Medical Co., Ltd. and IT convergence rehabilitation medical device research center of Korea Industrial Technology University. The electric wheelchair is a two-wheel drive type, unlike a typical mobile robot, the front two wheels are designed as a caster type so that the direction of the wheel can be adjusted when operating.

It has wide mechanism features for stable riding comfort of electric wheelchair user.

The appearance and size of the electric wheelchair used in the experiment are shown in Fig.

It is a foldable structure that is easy to store, and its size and weight are about two-thirds that of conventional electric wheelchairs.

15 is a configuration diagram of the electric wheel chair used in the experiment. There is a joystick that can be input by the user, a handlebar interface, and a display to check the speed and battery status around the interface. An electric motor and a gear box for rolling the wheels, and an encoder for calculating the number of revolutions of the electric motor, a battery and a controller for driving the electric motor, and a clutch serving as a side brake for the electric wheelchair. The overall hardware configuration of the electric wheelchair used in the experiment is shown in Fig.

The components used in the electric wheelchair system are the handlebar controller as shown in FIG. 16, the controller using Atmel's Atmega8, a force sensor for detecting the user's intention and an LED manual brake Respectively. The joystick controller controller uses Atmel's Atmega16, a joystick to determine the user's drive will, and an LED Array to indicate the speed of the LED Array battery. The STM32F407VG ST is used as the main controller, and it is equipped with current sensor, encoder, micro SD card, ultrasonic sensor, EEPROM and IMU sensor.

The specifications of the sensors required for the calculation of the electric wheelchair algorithm and the specifications of the sensor and the motor used in the electric wheelchair will be briefly described as follows.

The motor used is WOOSUNG's 24V DC motor. It has an output of 50W and has a rotation speed of up to 2200RPM. The end of the motor is connected to a gearbox with a ratio of 22: 1. Based on the above specifications, a safe RPM drive area can be created to safely use the electric wheelchair's motor.

The encoder used is H-40 series of LSIS, H40-6-0500ZO model. It has a rotation measurement resolution in which 500 pulses are measured in one rotation, and pulses are output in an open collector system. The main controller counts pulses output from the encoder in units of 10 ms and is used for control. The movement of the electric walking aids such as the speed of the electric wheelchair and the rotational angular velocity can be calculated through the counted encoder pulse information during 10ms.

17 shows information that can be collected according to the arrangement of the inertial sensor provided on the electric wheel chair.

The inertial sensor used in the experimental electric wheelchair is a six-axis IMU sensor. The three-axis gyro and three-axis accelerometer are synthesized by Withrobot's SD746 Breakout product. It is used to calculate various control values by transmitting information at a period of 10ms to main controller. Attach the inertial sensor to the center of the electric wheelchair to obtain the necessary information.

The experimental environment of the present invention uses the proposed route as shown in FIG. 18 so as to perform straight traveling, turning traveling, and mixed traveling. The actual path of the proposed experimental environment is shown in FIG. It is installed in the indoor flat path, and consists of 3m of straight path, 3.14m of turning path, and 5.14m of complex path. The material of the bottom surface is a conductive tile, which generally has a coefficient of friction of 0.5 to 0.6.

As shown in FIG. 19, the slip rate calculator of the straight line, the turnaround and the complex path, and the slip controller of the straight line and the complex path were experimented by different methods.

The slip rate calculator experiment was designed to allow the experimenter riding on the electric wheelchair to travel as much as possible. The specified path is a straight line, a turn, or a composite path. It collects information in real time wirelessly while driving according to the designated route. The experiment was carried out three times in total and the collected data were analyzed after the experiment.

Figure 20 shows the experimental results of the slip controller experiment in the composite path at the specified path

It is in progress.

The slip controller experiment in the room proceeded as follows. The experiment was conducted in two environments. The first experiment was conducted on a dry indoor road surface, and the second experiment was the same designated indoor path, but the indoor surface wetted with water drops an average of 0.1-0.4 more than the conventional coefficient of friction 0.5-0.6. Experiments were carried out by setting the ice on the wet road friction coefficient average 0.3 ~ 0.4. The experimenter who rides the electric wheelchair has to travel the designated route as much as possible. The specified route was performed three times for compound route driving. The collected data were analyzed after the experiment.

Basically, the acceleration information calculated by the encoder and the X-axis acceleration information measured by the inertia sensor are shown in FIG.

These two pieces of information represent the acceleration calculated by the X axis acceleration and the motor output information of the electric wheelchair in the straight running, and the difference of this information means the slip phenomenon in the straight path as summarized above.

22 is a graph showing a comparison between the gyro YAW axis information of the inertia sensor and the rotational angular velocity calculated from the encoder information attached to the motor. The difference between these two pieces of information is the slip phenomenon when turning the electric wheelchair mentioned above.

FIG. 23 is a slip ratio graph in a straight traveling state calculated based on the acceleration information calculated by the encoder information and the acceleration X-axis information of the inertia sensor.

It can be seen that the average slip rate during the specified route travel is less than 5%. However,

110 The value of the path information bounces is an error that shows a small error in the formula for changing the sensor information to the slip rate. It can be confirmed that there is some error but the slip observation is normal.

FIG. 24 is a slip ratio graph for turning traveling calculated based on the rotational angular velocity calculated by the encoder information and the gyro YAW information of the inertia sensor.

The average slip rate that occurs when an electric wheelchair rides on a turn wheel is 20%

. However, the error is detected in 140 ~ 150 area, which is the end point of the slip, which is an error that shows the small error among the formula that changes the difference between the sensor information and the slip rate like the previous error. It can be confirmed that there is some error but the slip observation is normal.

Fig. 25 shows the slip ratio of the composite path that is finally synthesized when the electric wheelchair is traveling. This comparison is made by comparing the slip ratio during straight traveling and the slip ratio information generated during swing traveling, and using a larger slip ratio.

In the state that the slip controller is operated, the traveling information on the straight road on the dry road surface is compared with the running information on the straight road surface on the wet road surface. Compares the driving information on the mixed route of the dry road surface and the wet road surface with the slip controller in operation.

Experiments were conducted on the designated straight path on the wet road surface. The first experiment deactivated the slip controller and proceeded with the experiment. In the second experiment, the slip controller was activated under the same conditions and the same path. The experimental results are as follows.

Fig. 26 is the actual traveling route information of the straight road section driving test in the wet road surface state as the first experiment. As the first experiment, the proposed slip controller was deactivated and tested. Experimental results show that, as shown in the above driving information, the user corrects the left and right path to compensate for the first right error after the standard solid line reference. However, since the slip ratio of the electric wheelchair is increased due to the running on wet road surface, the deviation of the path becomes more severe, and a path error of about 30 cm is found after 1 m of the straight path.

Fig. 27 is a traveling path in a straight section in a wet road surface state. The proposed slip controller is activated and tested. The second experimental result shows that the error is significantly reduced compared to the driving information when the slip controller is inactivated as a result of activating the slip controller. The error occurring in the section less than 50 cm after the start of the experiment is an error caused by the misalignment of the caster, which is the front wheel of the electric wheelchair, and the slip phenomenon occurs from the 150 cm section, but it can be seen that it does not deviate greatly from the path designated by the slip controller.

28 shows experimental results of wet road surface complex path slip controller states. A complex pathway experiment with a straight path turning section on a wet road surface was conducted. In the first experiment, the specified complex path on the wet road was run with the slip controller inactive, and the second experiment was performed after activating the slip controller. Experiments were carried out with the slip controller deactivated. Experiments were conducted on the traveling path without applying the slip controller proposed in the present invention. In the analysis of the travel route, it is necessary to turn to the right from 1m on the designated route. The slip phenomenon occurs, and the oversteer phenomenon occurs from the 0.6m portion, resulting in a large turning error to the left due to excessive turning.

29 is a composite route travel route information in a wet road surface state. The experiment was carried out with the slip controller activated. In this experiment, it is seen that the slip occurs in the straight section but the slip controller operates and hunts on the designated path. In the turning section, although the slip phenomenon occurs, it can be seen that the oversteer is reduced as much as possible and the vehicle travels on the designated route. It can be seen that the error to the final destination has been reduced from 1m to 0.4m compared with the inactivation of the slip controller.

According to the present invention, as a result of the slip controller test, it is possible to reduce a path deviation phenomenon caused by the slip phenomenon by more than half. In addition, the average slip rate is also reduced by more than half, thus securing the safety of the electric wheelchair on the wet floor of the indoor flat surface.

Although the present invention has been described in detail with reference to the above embodiments, it is needless to say that the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention.

The present invention is applied to a technique of detecting a slip ratio of an electric wheelchair and controlling the slip based on the detected slip ratio.

10: User input device
20: information detector
21, 22: first and second encoders
23: inertia sensor
30: Motor speed calculator
40: slip rate detector
41: Accelerometer
42: Slip ratio calculating unit
43: angular velocity calculator
44: Slip speed calculator
45: Turning slip ratio calculator
46: Slip ratio calculating section
50: Slip controller
51: Slip detector
52: Speed converter
60: Target velocity compensator
70: Motor speed controller
80: Motor

Claims

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A method of controlling slip of an electric wheelchair,
(a) receiving user's operation information, obtaining information of a motor driving a rear wheel of the electric wheelchair and actual speed information of the electric wheelchair;
(b) calculating a slip ratio based on the obtained information of the motor and the information of the electric wheel chair; And
(c) calculating a slip correction torque for controlling the slip based on the calculated slip ratio, and combining the slip correction torque and the target speed calculated according to the slip ratio to prevent slip by PID control of the motor and,
The step (c) includes the steps of: (c1) obtaining a final slip ratio; (c2) calculating a slip correction torque based on the obtained slip ratio, and calculating a motor control speed based on the calculated slip correction torque; (c3) driving the motor by PID control based on the calculated motor control speed,
(C2) calculating a motor control speed by adding the slip correction torque (correction value) to a target speed when the slip ratio is less than a first set value; (c22) calculating the motor control speed by subtracting the slip correction torque (correction value) from the target speed if the slip ratio is equal to or greater than the second set value; (c23) setting the motor control speed to the target speed when the slip ratio is equal to or greater than the first set value and less than the second set value.

[7] The method of claim 6, wherein step (b) comprises: (b1) calculating a slip ratio during a straight running based on the obtained motor information and the information of the electric wheel chair; (b2) calculating a slip ratio when turning on the basis of the obtained information of the motor and the information of the electric wheel chair; (b3) calculating the total slip ratio by combining the slip ratio during the straight traveling and the slip ratio during the turning travel calculated in the step (b3).

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