Design and Control of an Anthropomorphic Robotic Arm

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1 Journal Of Industrial Engineering Research ISSN Journal home page: (1): 1-8 RSEARCH ARTICLE Design and Control of an Anthropomorphic Robotic Arm Simon A/L Luthsamy, Haidar F. AL-Qrimli, Sharifah Shazzana Wan Taha, Nencent Raj A/L Luthsamy 1Department of Mechanical Engineering, Curtin University, Malaysia Address For Correspondence: Simon A/L Luthsamy, Department of Mechanical Engineering, Curtin University, Malaysia Received 3 January 2016; accepted 26 March 2016; published 3 May 2016 A B S T R A C T Background: In the 21st century, the design and development of robotic arms are being massively researched at the global level. One of the objectives of robotics engineering is to design a dexterous robotic arm whilst reducing the weight-to-payload ratio. Therefore, this paper highlights the mechanical design and electrical system concept and development of a 5 DOF robotic arm which is capable of human-like behaviors. Hence, these anthropomorphic characteristics are achieved via an ability to control the (i) shoulder (ii) elbow and (iii) wrist joints of the robot. Consequently, the robotic arm is infused with industrial knowledge thus possessing the ability to execute tasks such as the pick-and-place operation. The development of this robot is based on the Arduino UNO platform which is connected to the PS3-controller to operate the robotic arm wirelessly. The goal of the research is to deliver a robotic arm with minimum weight-to-payload ratio. Therefore, the current research proves that a light weight robotic arm is a viable option to sustain higher amount of payload and determine the robotic arm s capacity in serving its purpose. Key words: Robotic Arm; manipulator; degree-of-freedom; servo; payload; microcontroller INTRODUCTION Robotics is being constantly and extensively conflated into multiple lines of work superseding human labor thus performing persistent and durable tasks. Robotics is distinguished based on its types of application such as (i) Industrial (ii) Domestic or Household (iii) Medical (iv) Service (v) Military and (vi) Space. The term robot comes from the Czech word robota which means forced labour in Robotics is defined as the study and use of robot mainly for manufacturing [1]. One of the main objectives of robotics engineering is to design a manipulator capable of high dexterity. As for the industrial robotics applications, such as welding, painting, automated assembly, and pick-and-place are productivity related to the quality control [2]. Therefore a precise robotic manipulator needs to be achieved. Another fundamental concern of current robotics research has to develop anthropomorphic arms capable of emulating the dexterity, manipulability, weight-to-payload ratio and workspace. It is simple called an anthropomorphic arm because it has human like characteristics. The human arm consist a total of 7 Degree-of-Freedom [3]. DOF refers to the capacity of an object to move up and down, left and right and rotate. The up-and-down movement is called the Pitch whereas the left-and-right movement is called the Yaw. Meanwhile, the arm s rotating ability is termed as the Roll, as if you were using a screwdriver. Since the robot resembles the human arm, it has a base which enables it to rotate 180 degrees, connecting it to the manipulator above the base to represent that of a shoulder joint. Besides that, it has also rotational axes about its elbow and wrist joints [4]. An anthropomorphic arms not only be an ideal Open Access Journal Published BY IWNEST Publication 2016 IWNEST Publisher All rights reserved This work is licensed under the Creative Commons Attribution International License (CC BY). To Cite This Article: Simon A/L Luthsamy, Haidar F. AL-Qrimli, SharifahShazzana Wan Taha, Nencent Raj A/L Luthsamy. Design and Control of an Anthropomorphic Robotic Arm. Journal of Industrial Engineering Research,, 2(1): 1-8, 2016

2 2 Simon A/L Luthsamy et al.,2016 prostheses, but they would also make teleportation in undersea, space and also in hazardous environments that much easier for human to control. Literature Review: Light weight robotic(lwr) arms can be defined as robots with minimum own weight, particularly dedicated to tasks in location where its adaptability is necessary in relation to certain operation in an unstructured environment [5]. In order to achieve this, they are required to be light and the payload has to be equivalent/ simultaneous to its own weight. Human arm s motion differs from the motion of robotic arms [6]. Although the robot joints have lesser degrees of freedom compared to a human arm, they are able to move with larger angle. For an example, robot s elbow joint are able to bend up and down, whereas human elbow can only bend in one direction with respect to extended arm position. Vibration-free position control for a 2 DOF flexible-beam studied in the [7] aim to control the end of the flexible-beam by decreasing the vibration when the beam is subject to move. They have specially design the multi-axis force/torque sensor to control the system by using a reduced dynamic model. However, there is limitation in the motion and minimum workspace when in contact with the objects. Apart from that, a study on Design and Application of a 3 DOF bionic robot arm was carried out by the researcher [8]. The researcher claim that in order to lift high payload with high speed, the loose and deformed gears that occurs in the link should be eliminated. Tendon drive and fine motor control was developed in their paper to mimic the bionic arm structure. The arm consists of an elastically coupled drive which relieves the arm from bending forces. However, is requires additional control efforts for oscillation damping. Besides that, it is only comparable with small scale conventional manipulators with minimum payload. In relation to the study of robotic arm influence by the payload, another study is done involving potential energy in generating the human-like movement of robotic arm[9]. In their paper, they studied the production of trajectories of both end-effector and joints in order to achieve the reach-and-grasp motions just like a human arm. The human-like end-effector trajectory is traced by using Gradient Projection Method (GPM) while minimizing the total potential energy. This is to solve the kinematic redundancy of human arm in the target position. Another study on control system of mobile robotic arm was presented using wireless application [10]. By developing a wireless mobile robotic arm, the researcher expects to curb problems such as picking or placing an object from a distance from the user. Acrylic was used to fabricate the mobile robotic arm. The maximum payload capacity of the robot arm was tested to be 150 grams. The researcher has also recommended future work on upgrading the material used to lift higher payload. In this project we began by presenting the anthropomorphic robot arm design and prototype of 5 DOF jointed-arm robots. The design s aim is to perform an industrial task such as pick-and-place action. 6 servo motors were used to control the robot arm wirelessly, using a PS3 controller which able to lift maximum payload of 500g while maintaining minimum weight-to-payload ratio. Methodology: 1. Structure of Robotic Arm: The design procedure is divided in two major parts: a) The mechanical design b) The control system A) Mechanical design: The robot needs to be designed to mimic the movement of human arm. Therefore, this robot consists of robot base, shoulder, elbow, robot wrist and the end-effectors which will be the robot s gripper. This state-of-the-art knowledge is fulfilled by making it as perfect as possible [11]. Since this project involved the fabrication of human operation capabilities, there are several design requirements to be taken in consideration. Following are the robotic arm specifications: a) Revolute Jointed-arm b) Degree of freedom (DOF) = 5 c) Maximum range of motion per joint = <180 o d) 6 servomotors, one for the base, one each for the shoulder, elbow, wrist and two for the gripper. e) Payload capacity = 500g f) Material = ABS plastic I. Calculation for motor selection: After the structure of the robot arm is determined, motion for each joint needs to be developed. Therefore torque calculation is carried out for selecting the servo motors that drive the individual joints of the robot arm. Torque is defined as twisting force. It is calculated using the following equation:

3 Simon A/L Luthsamy et al.,2016 Moment = Force distance Kg-cm (1) Consider, Mass to be lifted = 500g Mass of upper-arm and forearm links = 11.51g Mass of wrist = 10.25g Mass of gripper = 2.

5) + (0.5 x 8.3) = 4.35 Kg-cm Elbow = (0.01151 x 4.5) + (0.055 x 5.95) + (0.02365 x 10.1) + (0.02785 x 13.5) + (0.5 x 16.3) = 9.15 Kgcm Shoulder = (0.01151 x 4.5) + (0.055 x 5.95) + (0.01151 x 12.

3 3 Simon A/L Luthsamy et al.,2016 Moment = Force distance Kg-cm (1) Consider, Mass to be lifted = 500g Mass of upper-arm and forearm links = 11.51g Mass of wrist = 10.25g Mass of gripper = 2.8g Length of upper-arm and forearm links = 8 cm Length of wrist links = 3.54 cm Length of gripper = 2.9 cm Gripper = ( ) x 2.9 = 1.46 Kg-cm Wrist = ( x 1.775) + ( x 2.5) + ( x 5.5) + (0.5 x 8.3) = 4.35 Kg-cm Elbow = ( x 4.5) + (0.055 x 5.95) + ( x 10.1) + ( x 13.5) + (0.5 x 16.3) = 9.15 Kgcm Shoulder = ( x 4.5) + (0.055 x 5.95) + ( x 12.5) + (0.055 x 13.95) + ( x 18.1) + ( x 21.5) + (0.5 x 24.3) = Kg-cm Therefore, the arm includes one MG958 servo motor at the shoulder, three MG946R servo motors at the base, elbow and wrist, and two MG90S servo motors at the gripper Fig. 1: Selected servos B) Control system: A part from mechanical design, electrical system used also to be taken into consideration. Electricity is the most common source of power and is used extensively with industrial robots. Following are the component used in this project. I. Microcontroller: An Arduino UNO is used to control all the 6 servos of the robot arm. Arduino is an open-source platform which is designed for prototyping projects. Figure 2 shows the Arduino UNO attached together with USB shield and Bluetooth adapter. Fig. 2: An Arduino Uno with USB shield II. Power Supply: The operating voltage of the Arduino board is +5v. This can be easily supplied by using the USB cable connected to the computer. Each individual servo also requires voltage supply of +5v. Arduino has a built in voltage regulator which supplies 5v but this single voltage output is not enough to power all 6 servos. Therefore,

4 Simon A/L Luthsamy et al.,2016 an alternate power source which is the CPU Power Supply Unit is used. The signal is sent by Arduino to the servo to position the arm.

Robot Configuration: Arduino IDE software is used to interface with the robot arm. A Bluetooth dongle is inserted to the USB shield and is programmed to connect to the PS3 controller wirelessly.

4 4 Simon A/L Luthsamy et al.,2016 an alternate power source which is the CPU Power Supply Unit is used. The signal is sent by Arduino to the servo to position the arm. Pin 5, 6, 7, 8, 4, 2 in Arduino is used for base, shoulder, elbow, wrist and gripper respectively. Fig. 3: Alternate power supply for servos Fig. 4: Schematic diagram of Arduino connection III. Robot Configuration: Arduino IDE software is used to interface with the robot arm. A Bluetooth dongle is inserted to the USB shield and is programmed to connect to the PS3 controller wirelessly. Therefore, the robot arm is controlled wirelessly using the controller to perform the desired task. Fig. 5: PS3 controller and its function programmed L1 = Ungrip L2 = Grip Left = Rotate gripper 90 0 Right = Rotate gripper = Rotate base 2 = Rotate shoulder 3 = Rotate elbow 4 = Rotate wrist

5 Simon A/L Luthsamy et al.,2016 2. Design of the arm: A. Base Design: The design of the robot s base is made to support the arm.

The base consists of lower base panel, supporting legs, mounting base (servo fixed), and rotating upper base panel.

5 5 Simon A/L Luthsamy et al., Design of the arm: A. Base Design: The design of the robot s base is made to support the arm. The base is designed to have a wider space to prevent the robot arm from flipping over when subjected to payload. The base consists of lower base panel, supporting legs, mounting base (servo fixed), and rotating upper base panel. The rotating base is connected to the servo which allows it to rotate at an angle +/- of 90 degrees from its mid position. Therefore, it will be able to rotate for a total of 180 degrees. Rotating upper base panel Supporting legs Mounting Lower base panel Fig. 6: The robot base B. Link Design: The arm is designed to mimic human the arm. Human arm consists of upper arm and forearm which are approximately the same length. Hence, in this project the arm and forearm link should be designed in such a way that they possess same length measurement. The aim of the arm design is to develop a light-weight arm. The length between both axes of rotation is 80mm and the total length of the links is 120mm. Fig. 7: The robot arm link C. Design of Wrist: The design of the wrist link also allows the link to rotate similar to the elbow joint. The purpose of the wrist link is to hold a mini servo at an angle of rotation similar to the base of the robot if all robot links are positioned vertically to the base. Mini servo is selected to rotate the gripper because there will not be much torque occur since the gripper will be installed directly near to the center of rotation without any offset length.

6 Simon A/L Luthsamy et al.,2016 Fig. 8: The robot wrist D. Design of The Gripper: To be able to grip/ hold an object and manipulate within the workspace of the arm at least 4 fingers are required.

An anthropomorphic design like the human finger allows task to be performed easily but the size and placement of each finger make the design heavier and control system to be complicated since each

6 6 Simon A/L Luthsamy et al.,2016 Fig. 8: The robot wrist D. Design of The Gripper: To be able to grip/ hold an object and manipulate within the workspace of the arm at least 4 fingers are required. However, the size and the placement of the fingers needs to be taken into account and also the task performed by the robot arm. An anthropomorphic design like the human finger allows task to be performed easily but the size and placement of each finger make the design heavier and control system to be complicated since each finger requires individual actuation. Therefore a non-anthropomorphic approach is considered to reduce weight, cost and simplify the design. The gripper design consist of two pincers that allow grip of an object and to lift it from the ground. The right pincer will be driven by the mini servo motor that connects the left pincer by a gearing system with pitch diameter of 20mm. Fig. 9: The robot s gripper RESULT AND DISCUSSION The robot with a stationary lower base and functional gripper has been built. The robot consists of 6 servo motors which provide 5 DOF. This will able it to move within the workspace. The base supports the entire arm which rotates about the shoulder. The revolute joint of the shoulder, elbow and wrist joint able to rotate about its axes. The mini servo that is attached to one of the gripper allows it to move the other part by the gearing system. Both the pincers move together in opposite direction and clamp to grip the object to be placed at desired location. Figure 10 shows the model of 5 DOF robot arm and its workspace.

A dumbbell weight of 500g was used to lift from the ground and is positioned to hold the payload. Figure 11 shows the robot arm holds the position while grapping the payload.

7 7 Simon A/L Luthsamy et al.,2016 Fig. 10: 5 DOF and workspace of the robot arm To evaluate the capability of the robotic arm and its objective, industrial application such as pick-and-place operation was carried out. A dumbbell weight of 500g was used to lift from the ground and is positioned to hold the payload. Figure 11 shows the robot arm holds the position while grapping the payload. The total weight of the arm was also measured, which is 792g. Fig. 11: Robot arm holds in position with payload of 500g Conclusion: An anthropomorphic robotic arm was designed and fabricated using Acrylonitrile Butadiene Styrene (ABS) to achieve a minimum weight-to-payload ratio that results about 1.6:1. The robotic arm consists of three main principle mechanisms: a shoulder, elbow and wrist joints. Each of the following mechanisms was optimized for strength, stiffness and minimum weight using finite element analysis from Solid Works software. Overall, the objectives of the project have been achieved which enable to control the robotic arm wirelessly and performing pick-and-place operation and also lifting a maximum payload of 500g within the workspace. Based on the study of weigh-to-payload ratio, it is beneficial for a robotic arm to have revolute joints since it requires links with less material and minimal torsional forces. Therefore, this makes the robotic arm to be constructed according to its specification while keeping the weight to a minimum. Besides that, light materials with high strength are advantageous for design of the robot base and the end-effector since major weight is from these two parts. Therefore, selecting a proper material for the production of these two parts results in dramatic weight reductions while maintaining the feasibility of the robotic arm. Future modification can improve the gripper by adding pressure sensor to avoid damage to the object.

8 8 Simon A/L Luthsamy et al.,2016 ACKNOWLEDGMENT The techinacal support of Curtin University Sarwak should be greatfully acknowleged. REFERENCES [1] Elfasakhany, A., et al., Design and development of a competitive low-cost robot arm with four degrees of freedom. Modern Mechanical Engineering, 1(02): 47. [2] Olson, C.F., Probabilistic self-localization for mobile robots. Robotics and Automation, IEEE Transactions on, 16(1): [3] Paik, J.K., et al., Development of an Anthropomorphic Robotic Arm and Hand for Interactive Humanoids. Journal of Bionic Engineering, 9(2): [4] Islam, M., M. Wazed and T. Mohammad, DESIGN AND FABRICATION OF A 5 DOF DEXTEROUS ROBOTIC ARM FOR INDUSTRIAL TASKS. pp: 58. [5] Hirzinger, G. and A. Albu-Schaeffer, Light-weight robots. Scholarpedia, 3(4): [6] Almurib, H.A., H.F. Al-Qrimli and N. Kumar, A review of application industrial robotic design. in ICT and Knowledge Engineering (ICT & Knowledge Engineering), th International Conference on. IEEE. [7] Castillo-Berrio, C.F. and V. Feliu-Batlle, Vibration-free position control for a two degrees of freedom flexible-beam sensor. Mechatronics, 27: [8] Klug, S., et al., Design and application of a 3 DOF bionic robot arm. regulation, 11: 12. [9] Zhao, J., B. Xie and C. Song, Generating human-like movements for robotic arms. Mechanism and Machine Theory, 81: [10] Yusoff, M.A.K., R.E. Samin and B.S.K. Ibrahim, Wireless mobile robotic arm. Procedia Engineering, 41: [11] Maas, S., Control of a pneumatic robot arm by means of reinforcement learning. Citeseer.

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