design and development of 6-dof robotic arm controlled by

Design and Development of 6-DOF Robotic Arm Controlled by Man Machine Interface

Sulabh Kumra1, Rajat Saxena1, Shilpa Mehta2 1 Department of Electronics and Instrumentation Engineering, ITM University, Gurgaon, India 2 Department of Electronics and Communication Engineering, ITM University, Gurgaon, India

E-mail: [email protected], [email protected], [email protected]

Abstract - This paper presents the design and development of a low cost and user friendly interface for the control of a 6-DOF slave tele-operated anthropomorphic robotic arm. Articulation of the robotic arm is achieved about six single-axis revolute joints: one for each shoulder abduction-adduction (abd-add), shoulder flexion-extension (flx-ext), elbow flx-ext, wrist flx-ext, wrist radial-ulnar (rad-uln), and gripper open-close. Tele-operator, master, uses the Man Machine Interface (MMI) to operate in real-time the robotic arm. The MMI has simple motion capture devices that translate motion into analog voltages which bring about the corresponding actuating signals in the robotic arm.

Keywords – Anthropomorphic, control, exoskeleton, man machine interface, robotic arm

I. INTRODUCTION

In this paper we aim to present the 6-DOF Robotic Arm controlled by the tele-operator using the Man Machine Interface (MMI) which is used by the tele-operator to control “DEXTO:EKA – the humanoid robot”[1], which is a human-scale tele-operated anthropomorphic robot. "Anthropomorphic" means having appearance like a human and "Tele-operated" means operated from a remote location.

Fig. 1 and Fig 2 shows the block diagram of Robotic Arm interfaced with the MMI using two atmel mega 2560 Microcontroller Units interfaced through XBee Pro units. Articulation of the robotic arm is achieved about six single-axis revolute joints: one for each shoulder abduction-adduction (abd-add), shoulder flexion-extension (flx-ext), elbow flx-ext, wrist flx-ext, wrist radial-ulnar (rad-uln), and gripper open-close[12]. The Man Machine Interface consists of an exoskeleton, graphical user interface and a mode selection switch which enables the tele-operator to select one of the three modes of operation. The three modes of operation are manual, semi-autonomous and autonomous. In manual mode, the tele-operator will have full control over the robot, thus disabling it to perform any action by itself.

In semi-autonomous mode, the tele-operator will still be the commander but the robot will reject the commands if they are dangerous for its survival. In autonomous mode, the robot will be autonomous and will perform live entertainment.

Fig. 1: Block diagram of Robotic Arm (Slave)

Fig. 2: Block diagram of Man Machine Interface (Master)

II. ROBOTIC ARM

The primary advantage of tele-operation is that homo-sapiens are adaptive and hence are compatible in dealing with unstructured environments. Specifically, this is an anthropomorphic robotic arm with 6-DOF (degree of freedom) [2]. The 6-DOF covers the major and most common arm movements to cover a large volume, and it also makes the arm easy to manoeuvre to

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lift and move objects in any orientationvery similar to a human arm with respecand positioning of joints. Of the six degrfour are for positioning (including the gfor orientation. If the joints are comhuman equivalent, then the robotic armhave the following joints: abduction (shoshoulder back and forth [3], elbow, wrispivot (wrist rotation), and gripper[7].

The actuators for all of these joints arTable 1 lists the number of motors used for each joint. There are in total ten sdifferent torques used[8][9]. The gripperconstruction; each finger with two parall

Force sensors are mounted between manipulator. These sensors measure strain placed on each of these joints. strain, the greater is the amount of forceexerting [6]. The main advantages of that it measures actual forces and that thdoes not interfere with the operationthemselves. It is appropriate, for the gripa force sensor to measure the amount ofis exerting on an object in its grip.

Fig. 3: 3D sketch of 6-DOF robot

To measure the force, a sensor is inside of one of the gripper prongs. Wcloses around the object, the sensor between the object and the gripper pronforce can be measured. These sensors arflexible circuit board and have a smallforce-sensitive ink. The resistance of thas the force applied increases [13]. By operational amplifier based circuit thiconverted into an analog voltage that one of the ADC inputs of the microcontr

n of space. It is ct to the number rees of freedom, gripper) and two mpared to their m can be said to oulder rotation), st up and down,

re servo motors. and angle range

servo motors of r is a two-finger lel links.

the joints of the the amount of The higher the

e that the joint is this system are he measurement n of the joints pper joint, to use f force the slave

tic arm

attached to the When the gripper

is compressed ng. From this the re mounted on a l circular dot of his ink increases y using a simple is force can be can be fed into roller.

DS18S20 one wire digattached at the gripper to meaobject and surrounding. DS[14] provides 9-bit Celsius tThe operating temperature +125°C.

Table 1 show the rangenumber of servo motors used

TABLJOINT RANGES AND NUM

Joint Ra(deg

Abduction 1

Shoulder 1

Elbow 1

Wrist 1

Pivot 1

Gripper N

Specifications of the Rob● Length: 68.5cm( Wh● Width: 4cm ● Weight: 2096gms (M● Load capacity: 500g● Degree of freedom:

The specifications of the ● Gripping size: 50mm● Gripping force: 500● Length: 110mm (W● Weight: 157gms (In

motors for gripping

Figure 4 show the actualarm for Dexto:Eka. The framade using aluminium alloy.

Fig. 4: Actual 6-D

gital thermometer is also asure the temperature of the

S18S20 digital thermometer temperature measurements.

range is from -55°C to

e of each servo motor and d for six joints of the arm.

LE 1 MBER OF SERVO MOTOR ange grees)

No. of Servos

105 2

130 2

125 2

180 2

180 1

NA 1

botic Arm are: hen straight)

Moving part only) gms 6 2 DOF gripper used are: m

0gms (Maximum) When fully closed)

ncluding 2 NRS-585 servo and twisting)

l developed 6-DOF robotic ame of the robotic arm is .

DOF robotic arm

2012 IEEE International Conference on Computational Intelligence and Computing Research

III. MAN MACHINE INTERF

Special emphasis has been given operation and some form of force sensatrig is fitted to the user’s arm. Use of a ‘a bilateral master slave control seintroduced to simplify the MMI Interface)[4][5].The prototype of the main Fig. 5 and Fig. 6, is aluminium alloy fuser straps onto his arm.

Fig. 5: 3D sketch of the MMI (Fron

Fig. 6: 3D sketch of the MMI (Sid

The designed sensing mechanism isaccurate and can be easily implemecontrol methodology, which has been usthe slave robot exactly replicates the motele-operator. Four potentiometers (resohm and of single turn) are placed on thone each at the wrist, elbow, abductiojoints[10]. The tele-oprators’ movempotentiometers, which produce an analoare fed to the ‘Master’ Atmel megcontroller unit and transmitted via a Xthe receiving XBee pro unit [15]. The rethen fed into the ‘Slave’ Atmel megcontroller wherein they are sampled an

FACE

to the ease of tion. The control wearable’ jig in

etup has been (Man-Machine

aster unit, shown frame which the

nt view)

e view)

s cost effective, ented. In MMI sed in our work, ovements of the sistance of 10k he master robot, on and shoulder ents rotate the og voltages that a 2560 micro-

XBee pro unit to eceived signal is ga 2560 micro-nd mapped into

corresponding actuating modulated signals) to actuate

Fig. 7: Man Mac

Figure 7 shows the Interface for the control arrangement is used to measjoint is commanded to movevoltage from the correspondThe Atmel 2560 mega microoperations of the humanoidindividual timers, hence thoperations rather than keepinThe inbuilt mapping functionthe Atmel 2560 mega mapsinto corresponding outputs tthe humanoid. All the elhumanoid is powered by a7.4V, 5000mAh, 30C dischar

IV. EXPER

We performed various performance and the accuracMMI. The gripper accuracyvarious objects and it wmaximum gripping size and50mm and 500gms respectiv

The 10 bit ADC on the Aanalog input into 10 bit digresolution). Since the servomarm have a maximum operatlevels are sufficient to maservomotor.

The work volume[17] ousing MatLab software. It hjoint angles computed, theprecision within ±0.5cm.

The current flowing into was determined and the resubelow. The torque produced

voltages (pulse width e the servo motors[11].

chine Interface

developed Man Machine of the robotic arm. This sure the positional error. A e to a certain angle, and the ding potentiometer is read. ocontroller used for control d has 14 PWM ports with he ALU is free for other ng track of the timer count. n in the wiring language of the analog voltage signals to drive the servomotors of lectronic circuitry of the

a Lithium Polymer 2 Cell, rge Battery.

RIMENTS

experiments to check the cy of the robotic arm using y test was performed using was determined that the d force of the gripper was

vely. Atmel 2560 mega maps the ital data (i.e.1023 levels of motors used in the robotic ting range of 180o, only 512 ap the entire range of the

of the arm was calculated as been found that with the e robot achieves position

the servomotors on the arm ult is recorded in the table

d by each servomotor on the


arm was determined and the result is recorded in the table below.

TABLE 2 JOINT SERVOMOTOR CURRENT AND TORQUES

Joint Torque (Kg-cm)

Current

(Amps)

Abduction 52.3 3.7

Shoulder 47.7 3.2

Elbow 32.6 2.4

Wrist 13.1 1.9

Pivot 8.4 1.2

Gripper 3.2 1.5

Fig. 8 shows the pick and place test[16] conducted, in which a 500gm object was picked from a table by the robotic arm and was placed back. The robotic arm was fully controlled using the Man Machine Interface (MMI), which was worn by Shilpa Mehta.

Fig 8: Picking and placing the object

V. CONCLUSION

In this paper, we presented the dynamical analysis and development of a 6-DOF[2] arm of an anthropomorphic tele-robot system controlled and commanded in real-time by a tele-operator in using the Man Machine Interface. The man machine interface was implemented on the real robotic platform. The presented model of the robotic arm has also provided correct joint angles to move the arm gripper to any position and orientation within its workspace. Results obtained from the model were compared with the actual performance of the robot in accomplishing a task e.g. pick and place of an object. It has been found that with the joint angles computed, the robot achieves position precision within ±0.5cm. This little deviation is because of many reasons namely, mechanical coupling of the joints, non-linearity in mapping angles to low-level encoder ticks.

ACKNOWLEDGMENT

We want to thank Dr Swaran Singh Ahuja and Assit. Prof. Ramandeep Singh for their guidance and all the team members and Junior Assistants for their support. We also thank ITM University for their financial support and providing labs with all the required tools and equipment.

REFERENCES

[1] S. Kumra, S. Mehta, “3D Modeling and Designing of Dexto:Eka:”, International Conference on Computational Vision and Robotics, Bhubaneswar, India, pp. 43-47, August 19, 2012


[2] C. Dong, G. Yang, Wen XU, “The real-time obstacle avoidance of seven freedom redundancy of humanoid arm”, Journal of Tsinghua university, vol. 10, 2004 [3] Kobayashi H, Ishida Y, Suzuki H, “Realization of all motion for the upper limb by a muscle suit”, IEEE International Workshop on Robot and Human Interactive Communication, Japan, pp. 631–636, September 20–22, 2004 [4] J. Iqbal, R. Islam, H. Khan, “Modeling and Analysis of a 6 DOF Robotic Arm Manipulator”, Canadian Journal on Electrical and Electronics Engineering, Vol. 3, No. 6, pp. 300-306, July 2012 [5] Kim Y S, Lee J, Lee S, “A force reflected exoskeleton-type masterarm for human-robot interaction”, IEEE Transactions on Systems, Man. and Cybernetics-Part A: Systems and Humans, Vol. 35, No. 2, pp. 198–212, 2005 [6] T. Sakaki, T. Iwakane, “Impedance control of a manipulator using torque-controlled lightweight actuators” IEEE Trans. Industry Applications, vol. 28, no. 6, pp. 1399-1405, Nov. 1992. [7] E. Torres-Jara, “Obrero: A platform for sensitive manipulation”, IEEE-RAS International Conference on Humanoid Robots, pp. 327–332, 2007. [8] H. Iwata, S. Kobashi, T. Aono, S. Sugano, “Design of anthropomorphic 4-dof tactile interaction manipulator with passive joints” Intelligent Robots and Systems, pp. 1785 – 1790, Aug. 2008. [9] J. Pratt, B. Krupp, C. Morse, “Series elastic actuators for high fidelity force control”, Industrial Robot: An International Journal, vol. 29, no. 3, pp. 234–241, 2002. [10] M. Zinn, B. Roth, O. Khatib, J. Salisbury, “A new actuation approach for human friendly robot design”, The international journal of robotics research, vol. 23, no. 4-5, p. 379, 2004. [11] D. Shin, I. Sardellitti, and O. Khatib, “A hybrid actuation approach for human-friendly robot design”, IEEE Int. Conf. on Robotics and Automation, Pasadena, USA, pp. 1741–1746, 2008 [12] Barrett Technology, Inc., “WAM Arm,” 2010. [Online]. Available: http://www.barrett.com/robot/products-arm-specifications.htm [13] Meka Robotics, “A2 compliant arm,” 2009. [Online]. Available: http://www.mekabot.com/arm.html [14] D. Shin, I. Sardellitti, and O. Khatib, “A hybrid actuation approach for human-friendly robot design”, IEEE Int. Conf. on Robotics and Automation, Pasadena, USA, pp. 1741–1746, 2008 [15] J. Stuckler, M. Schreiber, and S. Behnke, “Dynamaid, an anthropomorphic robot for research on domestic service applications”, Proc. of the 4th European Conference on Mobile Robots, 2009 [16] S. Robotics, “R17 5-axis robot arm,” 2010 [Online] Available: http://www.strobotics.com/ [17] M. Quigley, A. Asbeck and Andrew Y. Ng, “A Low-cost Compliant 7-DOF Robotic Manipulator”, International Conference on Robotics and Automation, 2011.

Mr Sulabh Kumra is pursuing his bachelor’s degree in Electronics and Instrumentation at ITM University, Gurgaon. He is currently the Joint Secretary of IEEE-ITMU. He is the founder member of Robotics Society of his university. His areas of interest are Embedded, Robotics and Automation. He

has always been a leader of many successful projects and is currently working on 'Dexto:Eka- The Humanoid Robot'. He has published research papers in International Journals and presented numerous papers in National and International Conferences. He has received Best Paper presenter award twice. He has been awarded with Young Investigator Award.

Mr. Rajat Saxena is currently a final year B.Tech (Electronics & Instrumentation) student graduating from Institute of Technology and Management University, Gurgaon, India. He has published research papers in the field of robotics in various science journals, IOSR Journal of Electrical and Electronics Engineering

(IOSRJEEE) and TJPRC to name a few and has received acceptance for publishing of his research papers in many international journals. His areas of interest include robotics, electronics and embedded systems.

Ms. Shilpa Mehta is pursuing her bachelor’s degree in Electronics and Communication at ITM University, Gurgaon. She is an active member of Robotics Society of her university. Her areas of interest are Coding, Embedded and Robotics. She has always been a cooperative and innovative member of

many successful projects and is currently working on her final year project- 'Dexto:Eka- The Humanoid Robot'. She has published research papers in International Journals and presented numerous papers in National and International Conferences. She has always been a part of all the technical events of her university.


design and development of 6-dof robotic arm controlled by

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