Design and Construction of a Mobile Robot with ...

International Journal of Materials Science and Engineering Vol. 2, No. 1 June 2014

Design and Construction of a Mobile Robot with Regenerative Brake on Dc Motors Juan Ruiz, Erika Torres, and Edwin Villarreal Universidad Manuela Beltrán/Vicerrectorí a de Investigaciones, Bogotá, Colombia Email: [email protected]

An industrial mobile DC-motor robot was implemened with 30Kg load capacity to test the regenerative break system. This system consists of: microcontroller, 12V batteries, power circuit, 2 DC motors, a recharge unit and a speed sensor (see Fig. 1). The speed control and recharge process are management by the microcontroller. 12V battery supplies the circuits and the DC motors. 2 DC motors moves and rotate the robot. The power circuit transfers the energy from the battery to the motors. The recharge unit transfers the energy from the motors to the batteries, and the speed sensor helps the microcontroller to maintain a constant speed.

Abstract—This paper presents the design and implementation of a mobile robot with regenerative braking system for DC motors. The DC motors converts the kinetic energy into electric energy when the robot is braking. The charging module increases the voltage generated by the motors using a boost DC-DC converter, along with a closed loop voltage regulation. The results proved that this system can use low generated voltages to charge the batteries, and it prevents high generated voltage to overcharge the batteries. The simplicity and reliability of this system, provides a low cost solution for robot mobile energy recovery. 

Index Terms—regenerative brake, energy recovery, mobile robot, recharge module, dc motor.

Microcontroller

I.

INTRODUCTION

Energy recovery systems recuperate energy from a subsystem or wastes. Nowadays, these systems can get energy form garbage [1] or kinetic energy on mobile systems [2]. Modern electric vehicles (EV) have systems to recover the kinetic energy during braking [3]. Most of these braking recovery methods recuperate the energy using a dedicated generator, besides the main motor [4]. Vehicle and robot regenerative systems are focused in the use of AC motors to recovery energy [5-6]. Xiao et al. [7] developed a DC motor recovery system. This system recovers the energy from series-wound brushed DC electric motors when the vehicle brakes to charge the batteries. Most of DC motor regenerate solutions do not use the regenerated energy when the generated voltage does not have the potential to charge the batteries, and they do not regulate the voltage to avoid overcharge the batteries. This paper presents the design and construction of a mobile robot with regenerative brake on DC motors. The brake system here development can convert the kinetic energy, during the braking, in electric energy to charge the battery through a recharge module. The recharge module consists of a boost DC-DC converter, which can support 24Ω load with 500mA, to increase the input voltage up to 12V to 14V, in order to obtain appropriate voltage charging levels. Besides, this module regulates the output voltage to avoid overcharging the battery. II.

P ower circuit

12V Batteries

Speed sensor

Rechargu e unit

Figure 1. Schematic diagram of industrial mobile robot

A. Mechanical Design A differential drive configuration [8] was chosen to move the robot. Two main wheels are in the back, each of which is attached to its own motor, and two more free wheels are in the front (see Fig. 2a). An aluminum structure was fabricated (60cm length, 40cm width and 25cm height) with 30Kg load capacity. The industrial robot must achieve 0.4m∕s top speed in 1 second on a 20° tilted plane. All forces on the robot should be considered to achieve the requirements. Fig. 2b describes the robot forces. The torque ( T ) required to get the robot moving has to be greater than the torque required for keeping it in motion. The sum of the forces acting on the robot will be equal the total mass multiplied by acceleration (see equation (1)).

ma  f  mgSin( )

DESIGN

(1)

Total robot mass (motors mass 2.7Kg, batteries mass 1.5Kg, structure mass 12Kg and load mass 30Kg) was calculated (total mass: m=46.2Kg). The force f is the mo-

Manuscript received December 12, 2013; revised February 17, 2014. ©2014 Engineering and Technology Publishing doi: 10.12720/ijmse.2.1.6-9

2 DC motors

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tor force ( f  T / r ), and  is the tilt angle. We obtain the motor torque form equation (1).

The recharge module consists of a boost DC-DC converter with a regulated output (see Fig. 3b). This converter increases the input voltage ( VI ) to an output voltage

15 cm

( VO ) suitable for charging the battery (more than 12V), and less than an overcharging voltage threshold (14V), with 500mA output current ( I O ). This converter works as follows: when Q1 is ON, current trough L1 is the maximum. When Q1 is OFF, current trough L1 is reduced. The reduction of this current produces a voltage on inductor L1 opposed to VI . The two sources ( VI and voltage

Front

40 cm

DC motors

on L1) are in series, and cause a voltage higher than the source to charge the capacitor C1 trough D2 [9]. P ower circui t

66 cm (a) Robot mechanical structure

Recharge module

Relay

Microcontroller DC Motor

(a) Motor switch for brake DC Mot or

V

I

(b) Robot forces in a tilted plane Figure 2. Robot structure and forces

ma 

II 1.5 mH

T  mgSin( ) r

T  ma  mgSin( ) r T  mr (a  gSin( ))

V

V S 1KHz D = 50% IO

(2)

T  6.5 Nm

O

RL Battery 24

(b) Recharge module circuit

The robot has two motors on the rear. Each motor must load 3.25Nm to fulfill the requirements. Two DC motors Matsushita GMX-8PV017D with 9.8Nm maximum torque, 143RPM speed and optical encoder was selected.

Figure 3. Recharge module

To calculate the circuit’s components we know that: VO is inversely proportional to 1  D ( D is the duty

B. Electronic Control A frequency voltage converter (LM2907N) was used to convert the motor speed to a voltage signal. This voltage signal is read by an ADC converter in the microcontroller (PIC16F877A). The microcontroller makes a digital proportional control to keep the robot at a constant speed by using two PWM signals which handle the motor power level.

cycle of VS ) [10].

VO 1  VI 1  D

(3)

Assuming the input power equal to the output power:

PIN  POUT

VI I I  VO I O

C. Recharge Process The recharge process takes place when the robot brakes. In that moment, the microcontroller disconnects the motors the from power circuit, and connects them to the recharge module (see Fig. 3a). The kinetic energy is transformed on electric energy by the motors, and this energy is transferred to the recharge module.

©2014 Engineering and Technology Publishing

IR

I O VI  I I VO IO  1 D II

7

(4)


the battery. The results are shown in Fig. 4a. When the motors generate more than 7V, the output voltage is elevated to an appropriate level for charging the battery (12.5V). If the motors generate more than 14V, the output voltage is regulated under 14V to avoid overcharging and damaging the battery. This module enables to charge the battery with voltages generated by the motors under the charge level. To test the mobile robot auto recharge, it was placed in a tilted plane with 35°degree slope. The battery voltage at the test was 11.5V. Five different loads weight were used. Fig. 4b shows the battery charging voltage and current values vs. load weight. When the load is increased, the voltage generated by the motors increases too, this in an inverted exponential curve between 7.3V and 11.8V. The charge current increases, when the charge voltage is near to the battery voltage level (the battery gets more current for charge). For this reason, the voltage growth rate decreases. Despite, low voltages generated by the motors (near to 7.3V) with a low load weight, the boost DC-DC converter lets the recharging module applies enough voltage to charge the battery.

The output current ( I O ) on the boost converter defined by Mohan et al. [10] is:

IO 

VO D(1  D)2 2 fL

(5)

To calculate L1, we know that I O = 500mA and f = 1KHz. Solving

L from Equation 5: VO D(1  D) 2 2 fI O

L

12V 0.5(1  0.5)2 2(1KHz )500mA L  1.5mH L

L1 and Q1 must support the max

(6)

I I =1A. D2 must

support the max I O =500mA. D1 is a 12V Zener diode. It puts the Darlington transistor Q2 on saturation when VO >12V. The Q2 saturation increases I R , and thus decreases I O , reducing VO . III. Rechargue mo

IV.

RESULTS

This paper presents design construction of a mobile robot with regenerative brake. This brake system can convert the kinetic energy, during the braking, in electric energy to charge the battery. In order to obtain appropriate voltage charging levels in low voltages at braking. The recharge module consists of a boost DC-DC converter, which can support 24Ω load with 500mA, to increase the input voltage up to 12V to 14V. Besides, this module regulates the output voltage to avoid overcharging the battery, by using a Zener-transistor based closed loop. The simulation results showed that the recharge module can keep an output voltage between the appropriate charging levels, with voltage inputs between (7V to 24V). The auto recharging capability was tested placing the mobile robot over a tilted plane with 35°slope, with different load weights. The results showed that the voltage and charging current increase when the load weight increases. The charging voltage growth rate decreases when it is near to the battery voltage level, and the charging current increases, charging the battery. The recharge module implementation for this mobile robot is an affordable and simple design; only requires two transistors, an inductor, one diode and one Zener diode. This system can be implemented in any DC motor based mobile robot, to regenerate the energy during the braking, without overcharging the batteries.

dule V in vs Vout

16 14 12

V out (V)

10 8 6 4 2 0 0

2

4

6

8

10 12 14 16 18 20 22 V in (V)

24

(a) Recharge module transfer function with an output load 24Ω. Battery charging levels 14

2

1.5

8 1 6 4

0.5 V in Ic

2 0

Battery charging current (A)

Batt ery chargi ng voltage (V)

12 10

REFERENCES

0 0

5

10

15

20

25

30

[1]

35

Load wei ght (Kg)

(b) Battery charging voltage and current results. Figure.4. Recharge results

[2]

The recharge module voltage transfer function (VO vs VI) was simulated on SPICE, with 24Ω load in place of

[3]


CONCLUSIONS

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D. Sasaki, K. Sasaki, A. Watanabe, M. Morita, Y. Igarashi, and N. Ohmura, “Efficient production of methane from artificial garbage waste by a cylindrical bioelectrochemical reactor containing carbon fiber textiles,” AMB Express, vol. 3, no. 1, pp. 17, 2013. M. Halley, “Kinetic energy recovery systems in formula 1,” ATZautotechnology, vol.8, 2008. S. A. Oleksowicz, K. J. Burnham, et al., “Regenerative braking strategies, vehicle safety and stability control systems: critical use-


case proposals,” Vehicle System Dynamics, vol. 51, no. 5, pp. 684699, Feb. 2013. [4] J. K. Ahn, K. H. Jung, D. H. Kim, H. B. Jin, H. S. Kim, and S. H. Hwang, “Analysis of a regenerative braking system for hybrid electric vehicles using an electro-mechanical brake,” International Journal of Automotive Technology, vol. 10, no. 2, pp. 229-234, 2009. [5] J. K. Xu, J. Q. Yang, and J. Gao, “An integrated kinetic energy recovery system for peak power transfer in 3-dof mobile crane robot,” In Proc. 2011 IEEE/SICE International Symposium on System Integration (SII), 2011, pp. 330-335. [6] R. E. Hellmund, “Regenerative braking of electric vehicles,” Transactions of the American Institute of Electrical Engineers, vol. XXXVI, pp. 1-78, 1917. [7] Y. Xiao, M. Nemec, L. J. Borle, V. Sreeram, and H. H. C. Iu. “Regenerative braking of series-wound brushed dc electric motors for electric vehicles,” In Proc. 2012 7th IEEE Conference on Industrial Electronics and Applications (ICIEA), 2012, pp. 16571662. [8] Y. Chung, C. Park, and F. Harashima, “A position control differential drive wheeled mobile robot,” IEEE Transactions on Industrial Electronics, vol. 48, no.4, pp. 853-863, 2001. [9] R. W. Erickson and D. Maksimovic, Fundamentals of Power Electronics. Springer, 2001. [10] N. Mohan and T. M. Undeland, Power Electronics: Converters, Applications, and Design, Wiley India, 2007.

ests are in the areas of, conservative energy, nanotechnology, atomic force microscopy, and microcontrollers.

Erika Torres was born in Bogotá, Colombia in 1986. She received the B.S. degree in electrical engineering in 2008 from the Francisco José de Caldas District University, Bogotá, Colombia, and the M.S.E.E. degree from University of Science and Technology of Beijing, China, in 2012. She is a Professor in the Department of Electrical and Computer Engineering, Manuela Beltrán University in Bogotá since 2013. Her research interests include algorithms for the analysis of signals and pattern recognition, analog control, and multidimensional statistics.

Edwin Villarreal was born in Bogotá, Colombia in 1979. He received his bachelor degree in design and electronic automation engineering from the La Salle University, Bogotá, Colombia in 2004. He received the M. Sc. Degree in Industrial Automation from the National University of Colombia, Bogotá, Colombia in 2008. From 2008 to 2013 he was a research teacher in the Electronics Engineering department of the Manuela Beltrán University, where he is currently the director of the engineering research department. His main areas of research interest are industrial automation and computational intelligence.

Juan Ruiz was born in Pasto, Colombia in 1984. He received the Bachelor degree from the Universidad de Nariño, Pasto, Colombia, in 2009; M.Sc degree in Electronic Engineering from the Universidad de Los Andes, Colombia, in 2012. He is a research professor in the Department of Electrical and Computer Engineering, Manuela Beltrán University in Bogotásince 2013. His current research inter-


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Design and Construction of a Mobile Robot with ...

Design and Construction of a Mobile Robot with ...

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