Development of Contactless Joystick for Low Speed Electric Vehicle

Vehicle Engineering (VE) Volume 2, 2014

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Development of Contactless Joystick for Low Speed Electric Vehicle Bo Wang*1, Jin-Woo Ahn2 Dept. of Mechatronics Engineering, Kyungsung University Busan, Korea *1

beyond.29@163.com; 2 jwahn@ks.ac.kr

Abstract Development of joystick driving control for low speed electric vehicle (LSEV) application is introduced in this paper. The joystick is proposed to replace the wheel steer in the conventional LSEV. The main advantages from the proposed algorithms are simplified the joystick characteristic through discriminated the driving area and braking area.

With this algorithm the driving resolution and capability area is improved. To verify the proposed algorithm, a simple prototype model which represents two electric motors for propulsion and steering was developed. This prototype utilizes the proposed method which proved the improvement of driving performance in the LSEV. Keywords Low Speed Electric Vehicle, Contactless Joystick, Control Algorithm

Introduction Electric vehicles, fuel cell electric vehicles and hybrid electric vehicles have been widely studied to improve fuel economy, emission and vehicle performance. A vehicle is consider “Green” when it more environmentally friendly than the traditional petroleum combustion engine, in which includes any non-traditional vehicle like, HEV, Plug-In EV, Fuel Cell, Bio fuel etc. that improves fuel economy. The development of electric vehicle has been over a hundred years but failure to gain the public acceptance in various stages due to various reasons which explained. While EV was never mass produced, Hybrid electric vehicle gains the momentum in recent years. Ford has launched its second generation of HEV and GM also announced the debut of the “Volt” in 2010. Comparing to the regular HEV, Plug in is the new trend in hybrid auto development due to extend travel range in electrical mode and a possibility of a zero emission as long as travel distance is less than the charging threshold. However, an electrification trend in automotive industry has been evolved and will

revolutionize the industry. With the correct policy and government help and advancement of electric vehicle technology, the prospect of Electric Vehicle will be bright and the focus point of future development. The differences between EV and LSEV are in the maximum speed and distance. With the maximum speed 40Km/h, LSEV enabled the economies, efficiency and smart transportation surrounding neighbourhood area [1-4].

In these years, electric vehicle is a new method for personal moving, going to work, and travelling.

However, a standard electric vehicle is designed to be driven by a normal person who is capable of using their arms and legs fast for controlling gas and brake pedals, a steering wheel, a shift lever. Some manual cars still need clutch pedals. However, in face of the incoming society of the aged, with the event is high many people began mobility, up, sit down, stoop become difficult moves. More and more elders in inconvenient action will use wheelchair. For senior people who have problems on their legs, a drive assist system, called hand control drive system, is now commercially available which enables a person to drive a car with no using their legs but use only left and right arms. At the same time, a control system which can control fast is required for slowly acting elders. In this paper, a developed control system in the conventional LSEV with joystick in the LSEV, a small group of severely disable people can accelerate, brake and steer a car with only using one hand, and thus regain a considerable proportion of their mobility.

This contributes to increased freedom and a higher quality of life.

Joystick Characteristic The joystick is a control device which combines steering, acceleration and brake control is one single lever. A joystick working based on integrates two different in formations in the same time with joining two degrees of freedom, forward-backward and

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Vehicle Engineering (VE) Volume 2, 2014

left-right. The handle is the primary control devices which can move 3600 rotation for make quick response on the track. The information, and more far, the vehicle, will moves in the same direction as the movement of joystick. The detail construction of joystick is shown in Fig.1.

(a)

(b)

FIG. 3 THE ELECTRIC CONFIGURATION OF GENERAL EV AND EV WITH JOYSTICK CONTROLLER

FIG. 1. DETAIL CONSTRUCTION OF JOYSTICK

The joystick used in this paper is a contact-less joystick type. The contact-less joystick turns the mechanical movement in the dandle into magnetic field variation through the permanent magnet (PM). This magnetic field then converted to the variation of voltages. The variates voltage then used as an input for motor controller and furthermore for control the rotation of the motor speed. The joystick output voltage characteristic is shown in Fig.2.

Y

Vehicle can e classified as an EV if there is at least one electric motor and electric motor and electric source imbedded as propulsion in the vehicle [5]. In general, EV only used one electric motor as the propulsion, while for steering, it still used a conventional hydraulic power steering. In this application where the joystick controls the acceleration and the steering movement, the conventional hydraulic power steering cannot be used. The steering in this application must be driven by the electric motor, so the EV movements (forward or backward) an EV steering (right or left) can be controlled though one single joystick handle.

The electric configuration of the general EV and the EV with joystick controller is shown in Fig. 3.

5V

Joystick Control Algorithm

R

x

α

0V

y 5V

X

2.5V

0V

The output voltage is variates along with the joystick movement. When the joystick handle is in the origin, the output voltage is equal t0 2.5 volts. The default characteristic of joystick causes the time used to reaches the maximum value of y and –y axis is same.

In fact, it is not necessary as the direction of a car is not often and suddenly changes.

FIG. 2 THE JOYSTICK OUTPUT CHARACTERISTIC

The maximum output voltage from the joystick is limited at 5 volts. With the aim to eliminate the negative voltage value, the origin point is set as 2.5 volts. With this condition, the minimum value of joystick movement is 0 volts. The joystick is free to move in any direction of working area (represented as the inside area of cycle in Fig. 2). Each point in the working area is represented two different in formations, the direction and speed in information.

This information obtained by the point distance from the origin R, and the angle which referred to the x-axis which denoted by α.

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Input

Outout

Delay timer

FIG. 4 RELATION BETWEEN INPUT AND OUTPUT OF JOYSTICK

The conversion from mechanical movement of joystick into variable voltage takes a little time. As a result,

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there is delay time between input trigger (mechanical joystick movement) and the output voltages. This delay time should be diminished with the aim to eliminate the control error and facilitate the ease driving of the vehicle. The relationship between mechanical joystick movement as an input and the variable output voltage is shown in Fig. 4.

đ??˝đ??˝đ?‘Ąđ?‘Ą =

đ??˝đ??˝ đ?‘ đ?‘ + ∑đ?‘˜đ?‘˜đ?‘›đ?‘› =1 đ??˝đ??˝ (đ?‘Ąđ?‘Ąâˆ’đ?‘›đ?‘› )

(1)

đ??žđ??ž+1

Percentage of the applicable arithmetic operations such as completion of differential input data, can be represented as the low-pass filter in electric circuit. k

To overcome this delay problem, the shortcomings joystick input are changed to the differential input data ΔP. The changed of general input signal to the ΔP is based on the adjustment ratio and average value of high reliability input joystick responses. The relationship between general input signal and differential input data is shown in Fig. 5.

FIG. 7 AVERAGE VALUE ALONG NUMBER OF K-SAMPLE

Input signal

As the joystick moves, the output coordinates as a function of radius R and angle ι these changes related with the number of sampling k for determine the average current data. The relationship between ΔP and k is shown in Fig. 7.

Almost not change

∆P

Major Change

t1

t2

∆P

t3

FIG. 5 RELATIONSHIP BETWEEN GENERAL INPUT AND DIFFERED DATA

The differential input data obtained from the comparison of the real time monitoring data and the average current data. So, if there is no difference between the real time data and the average current data, the input deferential data can be summarize as a single data. The differential value of the obtained data and the average current data are shown in Fig. 6.

The proposed algorithm improves the joystick performance up to 70% and furthermore the ease driving performance can be achieved. With the proposed algorithms applied in the joystick controller, the maximum output value of joystick in any condition can be achieved through a simple movement of joystick handle. The proposed algorithm causes the joystick characteristic change from cycle shape into eclipse shape. The proposed algorithm of joystick characteristic shape is shown in Fig. 8.

Y

Y

P Pn −1 ∆P

X

(a) Pn

FIG. 6 SCHEMATIC OF CURRENT AND REAL TIME DATA

where P is represent the real time monitoring data and Pn-1 is represent the current data. The different between P and Pn-1 then converted into percentage completion of the operation Js, the next future data Jt can be estimated. The relationship between Js, Jt and number of data sampling k is shown in Eq. 1.

X

(b)

FIG. 8 JOYSTICK CHARACTERISTIC OF: (A) GENERAL ALGORITHM; (B) PROPOSED ALGORITHM

Through the proposed algorithm, the sampling data can be reduced, so at the end the joystick is able to respond more protectively.

Implementation of Proposed Algorithm The replacement of the steering wheel, acceleration and brake pedal with the joystick required a new 17

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The algorithm is starting with the information of the driving direction (forward-backward), represented as a toggle-button in the flowchart. The behaviour of joystick controller will be changed as the button changes. When the vehicle is in the forward condition (button=0), the –y zone in the joystick characteristics (see Fig. 8) is becomes braking zone. Vice versa when the button equal 1 (button=1) or in the reverse direction, the y area become the brake zone. With implement the proposed method, the braking are of any direction will be shorter than the driving area, its mean, to achieve the maximum braking point, less of time and little movement of joystick is needed, and the behaviour and braking zone of the joystick with the proposed method are shown in Fig. 10. θ = Joystic position on the x-axis

Start

r = radius of joystick coordinate

N

Button=0

Y

−1800 < θ < 0

Y

N

R _ Speed = r ⋅ ( R e v _ Func(θ )) Wheel _ angle = θ

N

0 < θ < 1800 Y

F _ Speed = r ⋅ ( Frwd _ Func(θ )) Wheel _ angle = θ

Brake _ level = r Wheel _ angle = θ

End.

FIG. 9. THE FLOWCHART OF PROPOSED ALGORITHM

Brake zone

s

s

θ

Brake zone

(a)

(b)

FIG. 10 BRAKING ZONE FOR (A) FORWARD DIRECTION; (B) REVERSE DIRECTION

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Brake zone

r

Speed

control algorithm to control the vehicle. Three separated different control functions in the conventional LSEV combined into one controller with the same capabilities. The proposed algorithms include the steering (right and left), the acceleration and the brake functions in one control handle. The flowchart of proposed algorithm is shown in Fig. 9.

Brake

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0

900

1800

2700

3600

θ

FIG. 11 BRAKING AND DRIVING CHARACTERISTIC

Applying the proposed method to the joystick affects to the breaking characteristic. This characteristic made the radius (see Fig. 11) of data in the reverse direction is minor change and almost flat in any y direction.

This condition is helpful when the panic or suddenly brake of the vehicle. While in the driving zone, the steering of joystick can move smoothly due optimize and larger area. The relationship between the braking and driving condition of the optimized method is shown in Fig. 11.

Experimental and Measurement To verify the proposed algorithm, a simple prototype which represents two electric motors for propulsion and steering was developed. The prototype model employed one 4/5 switched reluctance motor (SRM) for propulsion and one servo motor for the steering. A 12 volts of DC power is used for supplying the motor drive. As the system build, a measurement of the proposed algorithm performance was executed.

The maximum output voltage of joystick is 5 volts.

This maximum volt then converts as a command for the propulsion motor to rotate in maximum speed.

The maximum speed of propulsion motor is limited at 1000 rpm. The maximum speed of propulsion motor is limited at 5000 rpm, while for the steering motor is limited at 1000 rpm. The lower maximum speed of the steering motor is due the needs of high resolution movement in the steering wheel.

The prototype model of LSEV with joystick controller is implement one toggle button. The toggle button is used to changes the direction of propulsion motor, forward or backward direction. At the same time the joystick controlled the propulsion motor speed, it is also controlled the movement of steering motor, so at single movements of joystick, two motors are controlled.

If the joystick moves along the maximum positive curve (see Fig. 10 (a)), then the propulsion motor will rotates from 0 rpm and smoothly increase to 5000 rpm when the joystick achieve 90 degree. Then reduce to 0

Vehicle Engineering (VE) Volume 2, 2014

rpm as the joystick circular movement from 90 degree to the 180 degree. The relationship of output joystick characteristic or joystick command, actual motor speed, the joystick position and toggle button single is shown in Fig. 12. It be imagined as the LSEV which smoothly moves form 0 rpm to the maximum speed increased gradually, while, the steering wheel rotates from maximum right direction to the 0 direction. Then, as the button signal changes, the propulsion motor direction is changed. The changed direction of the propulsions motor can be seen as the inverse direction of joystick command and actual motor speed into negative values.

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known as braking condition. At the braking region, movement of joystick will result the same value as maximum braking.

The prototype of LSEV with joystick controller proves the improvement characteristics of joystick driving control for LSEV. The proposed algorithm provides an ease driving characteristic for the user.

Conclusion The development of joystick algorithm for LSEV application is introduced. The replacement of steering wheel with the joystick required a new control algorithm. With the aim to help disabled people, an improvement characteristic though the proposed algorithm of joystick is applied. The proposed algorithm provides reduce of delay time and working time in the inverse direction due to changed of joystick region characteristic.

ACKNOWLEDGMENT

FIG. 12 RELATIONSHIPS AMONG ACTUAL MOTOR SPEED, JOYSTICK COMMAND, JOYSTICK POSITION AND BUTTON SIGNAL

Fig. 12 shows the relation between joystick command and button signal with no brake condition. The proposed algorithm sustains the brake condition with the small movements of joystick into inverse direction.

The relationship among the joystick position and actual motor speed in driving and braking region is shown in Fig. 13.

This research was supported by the Ministry of Education (MOE) and National Research Foundation of Korea (NRF) through the Human Resource Training Project for Regional Innovation and BK21plus.

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Larminie, J., Lowry, J. (2003). Electric Vehicle Technology

FIG. 13 RELATIONSHIPS AMONG ACTUAL MOTOR SPEED, JOYSTICK COMMAND AND JOYSTICK POSITION IN THE DRIVING AND BRAKING REGION

As the joystick moves smoothly along the maximum positive curve (see Fig. 10(a)), the propulsion motor will rotates gradually increase until the joystick at 90 degree. At 90 degree of joystick position, the propulsion motor rotates at maximum speed. The reducing gradually until the joystick achieves 180 degree. The joystick movement over than 180 degree is

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