Control Algorithm for a Biped Robot Based on Servo-Motors Controlled by an Android Application Ch´ avez avez Ariel, Fern´andez andez Andrea, Machado Luis, Revelo Jefferson July 10th, 2015 knows the enormous complexity of designing a robotic system, as may become a robot arm, which has 6 DOF. In the case of a humanoid robots that fact go even further, as there are systems with more than 30 DOF, which gives the system a high mobility but this require a high computational load in the control system. This implies a high cost in most most bipedal bipedal robotic robotic systems systems designed designed until these days.
Abstract
This This paper paper pres presen ents ts the the concontrol of a bipedal robotic platform. The design design presen presented ted is capabl capablee of forward movement, the robot is able to walk walk repetitive repetitively ly,, also detects tects and dodges obstac obstacles les.. Also Also presents presents a control control algorithm algorithm that acti activ vate ate the kick kick secu secuen ence ce.. The The robo robott can can be con control trolle led d in two ways: ways: manually manually or automatic automatically ally with with an Android Android applic applicati ation. on. To obtain these movements has been implemen implemented ted a basic control control system, tem, determ determine ined d by a genera generator tor of movemen movementt patterns. patterns. The main objective to be pursued with the design of this robot is to get a robust electronic platform.
In general, a bipedal locomotion system consists of several members that are interconnected with actuated actuated joints. In essence, a man walking robot is nothing more than a robotic manipulator with a detachable and movin movingg base. base. The design design of bipedal robots has been largely influenced by the most sophisti phisticate cated d and versat versatile ile biped known known to man, man, the the man man hims himsel elf. f. Th Ther eref efor ore, e, most most of the models/machines developed bear a 1. INTRODUC INTRODUCTION TION strong resemblance to the human body. AlIn recent years it has been noted how most any model or machine can be characrobotics has begun to cease to belong ex- terized as having two lower limbs that are clusively to the industrial world, push out connected through a central member. into into the dail daily y life life of people people.. Th Thee roboti roboticc starts to open a large number of possibilAlthough the complexity of the system ities, ities, such such as virtual virtual pets, p ets, micro-c micro-clean leaning ing depends on the number of degrees of freerobots, etc.; limited only by the human ca- dom, the existence of feet structures,upper pacity pacity to carry carry them out. One possibili possibility ty,, lim limbs, etc., etc., it is widel widely y know known n that that even even which for decades man has imagined, but extreme extremely ly simple simple unactuat unactuated ed systems systems can could not carry out until a few years ago, generate ambulatory motion. has has been perfor performi ming ng a robot robot with with mov movements like a human, with the same or very simila similarr motion charac characteri teristi stics. cs. Every Everyone one Thus Th us,, this this paper paper presen presents ts a desig design n of 1
the lower extremities of a biped robot with The robot has the ability to mobilize a robotic system of low cost and high inter- their ankles, knees and hips, right and left, connection capacity. controlling the motors of each ankle.
2. BIPED ROBOT DESIGN
Bipedal robotics platform used was called by its manufacturer as ”BRAT” meaning Bipedal Robotic Articulating Transport, it has six degrees of frees (6 DOF); two ankles: right and left, two on his knees: right and left and two on its hips: right and left.
Fig.2: Ankle’s move
The robot moves its knees sideways, and have big feets to give better stability while it makes the walking routines.
Fig.1: Degrees of freedom of the biped robot
This bipedal platform has a basic similarity to the human structure, it is constructed of anodized aluminum. The bipedal platform has the ability to make several moves: move forward, turn left or right as basic moves, being able to perform several routines movements. It presents a great stability because the robot support surface has a large area, compared to the length of his legs. This robot can detect obstacles using an ultrasonic sensor.
Fig.3: Knee’s move
2.1. Degrees of Freedom(DOF) The degrees of freedom that owns the platform are generated by six servomotors (HS-422) to move each of the joints: ankle, knee, hip, both left and right. Fig.4: Hip’s move
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Materials and devices used will be shown in the next chapter.
3. HARDWARE
Bipedal platform called BRAT has two operating modes: manual mode, where the robot is controlled by an Android application, and automatic mode, in which the robot is not led by any user.
Fig.7: Servo-motor HITEC HS-244
To detect objects at a distance under 20 ATMEGA8 microprocessor is used as cm, the robot uses an ultrasonic sensor. the robot’s brain. This microprocessor handles all the peripherals that owns the platform such as servo motors, ultrasonic sensor and also perform Bluetooth communication with an Android device.
Fig.8: Ultrasonic sensor
To communicate the bipedal platform with the Android application a Bluetooth module was used.
Fig.5: ATMEGA8
ATtiny 13A microcontroller was chosen for the task of sensing the distance with the ultrasonic sensor, and to uncouple the motion control program and the obstacle detection program.
Fig.9: HC-05 Bluetooth 4. DEVELOPMENT OF CONTROL PROGRAM
Fig.6: ATtiny 13A
Both, the principal microcontroller(Atmega8), that was used for control For articular movements six actuators the biped; and microcontroller ATtiny, used are used, which allow different movement for control the ultrasonic sensor; were proroutines. grammed in ATMEL STUDIO 6.2, while 3
the application for wireless communication was developed in App Inventor. The schematic diagram of the control circuit shown in the picture below, shows the connection of motors, ultrasonic sensor and bluetooth.
Fig.11: Android application
To understand the control program, main loop program flow chart are shown below. This show the different funtions that have the biped robot, like serial comunication, detection of obstacles, motors control and the main program
Fig.10: Control circuit diagram
The control program is performed with 4 subroutines contained in tables. There is a table to walk, another to turn right, one to turn left and the last one allows kicking. When ultrasonic sensor detects an obstacle at a distance of 20 cm, sends a 1L signal to the main microcontroller, this makes the robot interrupted its walk and turn. The interface developed for robot control allows to select two modes of operation, manual and automatic; in manual mode has options like walking, turn right, turn left and kick. The microcontroller receives a command to select any of these options and reacts to the order received. Android application is shown in figure below
Fig.12: Main progam loop
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First , we created a table of sequences that allow the robot to perform different actions after that we configure the timers, the USART and interruptions . We check if the user wishes to work in manual or automatic mode , and depending on this, the orders are executed.
Fig.14: Obstacle detection routine
Fig.13: Timer interrupt routine
The timer interrupt routine has a counter which is incresed and the pulse width of each PWM is verified, when the pulse width is greater than the pulse width set the pin is put in 0L.
Fig.15: Serial comunication routine
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5.3. Biped kicking
Fig.16: Ultrasonic sensor flowchart 5. RESULTS
Fig.19: Biped kicking.
5.1. Biped walking 6. CONCLUSIONS
The robot varies his rotation time depending of the surface on which the robot is walking, in rough surfaces rotates faster than on smooth surfaces , in the last ones the robot starts to skid , for this reason it takes longer to turn. Likewise, the walking is much better on a roughened surface than in a smooth surface . It was possible to get the target set to develop an automatic mode with motion detection and obstacle avoidance. Fig.17: Biped walking
An influential factor was the development of the motion sequences including the weight of the batteries, as these cause the center of mass of the robot varies differently.
5.2. Biped turning
The power consumption of the actuators is considerable, so it was decided to use an independent source for the microcontroller, in order to avoid brownouts that reset the control system.
BIOGRAPHY
Fig.18: Biped turning
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Ch´ avez Ariel:
eas of interest: Industries systems, domotic, robotics and microcontrolled sistems
He was born in Ba˜ nos - Ecuador. He completed his secondary education at the San Alfonso high school. He studies at the National Polytechnic School career in Electronics and Control Engineering. He qualified Adequacy CEC. Areas of interest: robotics, computer science, micro controllers, industrial automation and control.
Revelo Jefferson:
He was born in Ibarra - Ecuador. He completed his secondary education at Technic San Jos´ e hihg school.He studies at EPN Electronic and Control engineering. Areas of interest: Industries systems and security systems.
Fern´ andez Andrea:
she was born in Tabacundo Ecuador. She completed her secondary education at the Instituto Tecnologico Superior Nelson Torres. She studies at the National Polytechnic School career in Electronics and Control Engineering. She qualified Adequacy CEC. Areas of interest: computer science, microcontrollers, industrial automation and control.
References [1] Atmega8 Datasheet [2] Herrera Marco,’Ensamblaje y Control de una plataforma B´ıpeda mediante un PC’,Quito, 2009 [3] Candelas Francisco,’Servomotores’, Universidad de Alicante, 2007 [4] Seungmoon Song,Joohyung Kim, and Katsu Yamane,’Development of a Bipedal Robot that Walks Like an Animation Character’
Machado Luis:
He was born in Guaranda - Ecuador . He completed his secondary education at the Colegio Centenario Nacional Pedro Carbo. He qualified Adequacy CEC. He studies Electronic and Control engineering at EPN. Ar-
[5] Announced Specification of HS-422 Standard Deluxe Servo [6] Announced Specification of HS-311 Standard Deluxe Servo [7] Vaidyanathan.V.T and Sivaramakrishnan.R, ’Design, Fabrication and Analysis of Bipedal Walking Robot’,Department of Production Technology, Madras Institute of Technology, Anna University, INDIA
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