AUTONOMOUS MOTION CONTROLLED HAND-ARM ROBOTIC SYSTEM

Transcription

1 Autonomous Motion Controlled Hand-Arm Robotic System AUTONOMOUS MOTION CONTROLLED HAND-ARM ROBOTIC SYSTEM NIJI JOHNSON AND P.SIVASANKAR RAJAMANI KSR College of Engineering,Thiruchengode Abstract: This paper presents the design and characteristics of an autonomous motion controlled hand-arm robotic system. The hand-arm robotic system is using haptic technology. The haptic interface, which consists of a robot arm and hand, can be used in a large workspace and can provide multipoint contact between the user and a virtual environment. The system consists of three main modules that is the Data Glove with flex sensors and Micro-Electro Mechanical System (MEMS), the robotic hand with a six Degrees of Freedom (DOF) of movement and microcontroller (MCU) which will monitor sensor signals and sends the control variables to the servo controller and finally the actuation is achieved by servomotors. Servo motors can be used for motion. The system works on two modes, manual mode and in automatic mode. In manual mode it has keypad which controls the motion and has also got six servomotors which controls the direction. Its precision positioning makes it ideal for robot arms. In automatic mode flex sensors and MEMS giving the current position of master arm to the microcontroller. The haptic technology based system optimized on simple, less expensive and practically usable robotic arm. The aim of the system is to perform simple tasks i.e. lifting and moving simple light weighted objects, the system can be used in automated industries and tele robotics. I. INTRODUCTION Robotics is the science of designing and building robots suitable for real-life applications in automated manufacturing and other nonmanufacturing environments. Robots are meant to aid people, making a task easier or aiding a person who wants or needs help. The main use of robots has so far been in the automation of mass production industries, where the same, definable tasks must be performed repeatedly in exactly the same fashion. The arm control by robotics is very popular in the world of robotics. A robotic arm is usually programmable with similar functions to a human arm. Robotic arm can be used to perform a variety of tasks with great accuracy. Haptic technology is using in the hand-arm robotic system. * john.nijijohnson@gmail.com Haptics is a term that was derived from the Greek verb haptesthai meaning of or relating to the sense of touch [1], [2]. It refers to the science of manual sensing and manipulation of surrounding objects and environments through the sense of touch. The touching of objects or environment could be made by humans, machines, or a combination of both; and the objects and environments can be real or virtual or a combination of both [4]. Haptic devices are expected for two types of systems [3]. They are Virtual Reality (VR) systems and Master-Slave systems. Virtual reality systems are expected for use in surgical simulations and for various training applications. On the other hand, master-slave systems are applied for tasks that are difficult for human to execute, such as dexterous micro operation and operation in extreme environments like cosmic space, inside nuclear reactors, etc. The Degrees I J E E E S, 4(1) June

2 Niji Johnson and P. Sivasankar Rajamani Of Freedom (DOF) is very important in robotic arm [6], [7]. Each degree of freedom is a joint on the arm, a place where it can bend or rotate or translate. Robot arms are often categorized by their degrees of freedom (typically achieving more than six degrees of freedom). The number typically refers to the number of single-axis rotational joints in the arm. II. SYSTEM ARCHITECTURE The system architecture can be divided into two sections as hardware architecture and software architecture. The robotic arm s main components are the arm itself, which may have several segments; the joints (called axes), which are located between segments; the hand (called the end effectors or end-of-arm tooling).the robotic arm is mounted on a base that can be installed on the floor, ceiling, or wall or in a metal framework. The arm also has a power source, most commonly an electric motor, and it has wiring and various electrical and electronic components that allow it to perform its functions, direct it, and enable operators to interact with it. The following section gives a brief idea about the both of the architectures. (A) Hardware Architecture The hardware section contains a microcontroller which acts like the brain of the system. In the system ARM7 is used, an advanced and cost effective microcontroller well suited for applications due to its tiny size, low power consumption, high reliability and efficiency. The flex sensors are used to detect bending or flexing, that change in resistance depending on the amount of bend on the sensor. MEMS are used to provide multi axis sensing and more accurate data, which can detect acceleration, inclination and vibration. The block diagram of the system is given by figure1. The arm control by robotics is very popular in the world of robotics. The essential part of the robotic arm is a programmable microcontroller. The microcontroller is the core of the system. Figure 1: Block Diagram Outputs of these sensors are processed by a microcontroller. ARM7 has the advantage of high processing power which ensures reliability and also it has enough internal memory. It can work up to 60MHz speed and RISC architecture accounts for its popularity. Peripherals like PWM 1, UART 2 and PORTS are ideal for the system. The robotic hand-arm consists of six servos. The system carries an embedded system board. The robotic hand-arm system can be controlled either manually or automatically. In auto mode the commands are stored in EEPROM memory, and in the manual mode the robotic arm movements are controlled with switches. 1. PWM-Pulse Width Modulation 2. UART-Universal Asynchronous Receiver Transmitter EEPROM stands for Electrically Erasable Programmable Read-Only Memory and is a type of non-volatile memory used in electronic devices to store small amounts of data that must be saved when power is removed. EEPROM is usermodifiable Read-Only Memory (ROM) that can be erased and reprogrammed repeatedly through the application of higher than normal electrical voltage generated externally or internally in the case of EEPROMs. EEPROMs were limited to single byte operations which made them slower. EEPROMs are realized as arrays of floating-gate transistors. The main input to the microcontroller is the keyboard, flex sensors and MEMS. The function 30 I J E E E S, 4(1) June 2012

3 Autonomous Motion Controlled Hand-Arm Robotic System of the keyboard is to control the microcontroller manually. MEMS are a tilt sensors to measure the angle to identify how much angle the handarm is tilted. The flex sensor is used to detect bending or flexing, the change in resistance depends on the amount of bend on the sensor. The microcontroller has six output ports which controls the servomotors. Servo motors can be used for motion. Most servo motors can rotate about 0 to 180 degrees. The system consists of three main modules that is the Data Glove with flex sensors and MEMS, the robotic hand with a six DOF of movement and MCU which will monitor sensor signals and sends the control variables to the servo controller and finally the actuation is achieved by servomotors. The flex sensors data and MEMS data is captured by MCU and transmitted wired or wirelessly to the actuation side. The Robotic hand is capable of performing pitch and roll action and actuation of fingers. The code running on the MCU regularly reads the analog signals coming from the data glove and converts them to a digital value using internal ADC and mapping the respective reading to the respective servo motors to achieve the desired angle. The ARM7TDMI-S is a general purpose 32- bit microprocessor, which offers high performance and very low power consumption. The ARM architecture is based on Reduced Instruction Set Computer (RISC) principles, and the instruction set and related decode mechanism are much simpler than those of micro programmed Complex Instruction Set Computers. This simplicity results in a high instruction throughput and impressive real-time interrupt response from a small and cost-effective processor core. Pipeline techniques are employed so that all parts of the processing and memory systems can operate continuously. Typically, while one instruction is being executed, its successor is being decoded, and a third instruction is being fetched from memory. The ARM7TDMI-S processor also employs a unique architectural strategy known as THUMB, which makes it ideally suited to high-volume applications with memory restrictions, or applications where code density is an issue. The key idea behind THUMB is that of a superreduced instruction set. Essentially, the ARM7TDMI-S processor has two instruction sets: The standard 32-bit ARM instruction set. A 16-bit THUMB instruction set. The THUMB set s 16-bit instruction length allows it to approach twice the density of standard ARM code while retaining most of the ARM s performance advantage over a traditional 16-bit processor using 16-bit registers. This is possible because THUMB code operates on the same 32- bit register set as ARM code. MEMS accelerometers are one of the simplest but also most applicable micro-electromechanical systems. An accelerometer is an electromechanical device that measures acceleration forces. These forces may be static, like the constant force of gravity pulling a tour feet, or they could be dynamic caused by moving or vibrating the accelerometer. It outputs three analog values corresponding to the X, Y & Z direction coordinates. Figure 2 shows MEMS board. Figure 2: MEMS Board The device consists of two surface micro machined capacitive sensing cells (g-cell) and a signal conditioning ASIC contained in a single integrated circuit package. The sensing elements are sealed hermetically at the wafer level using a bulk micro machined cap wafer. I J E E E S, 4(1) June

4 Niji Johnson and P. Sivasankar Rajamani The g-select feature allows for the selection among 4 sensitivities present in the device. Depending on the logic input placed on pins 1 and 2, the device internal gain will be changed allowing it to function with a 1.5g, 2g, 4g, or 6g sensitivity. The 3 axis accelerometer provides a Sleep Mode that is ideal for battery operated products. When Sleep Mode is active, the device outputs are turned off, providing significant reduction of operating current. Flex sensors are sensors that change in resistance depending on the amount of bend on the sensor. They convert the change in bend to electrical resistance the more the bend, the more the resistance value. They are usually in the form of a thin strip from 1"-5" long that vary in resistance. They can be uni-directional or bidirectional. The resistance range can vary from 1K-200K ohm. They are often used in gloves to sense finger movement.figure 3 shows the working of flex sensors. Servos are extremely popular with robot, RC plane, and RC boat builders. Most servo motors can rotate about 90 to 180 degrees. Some rotate through a full 360 degrees or more. However, servos are unable to continually rotate, meaning they can t be used for driving wheels (unless modified), but their precision positioning makes them ideal for robot arms and legs, rack and pinion steering, and sensor scanners. Since servos are fully self contained, the velocity and angle control loops are very easy to implement, while prices remain very affordable. To use a servo, simply connect the black wire to ground, the red to a 4.8-6V source, and the yellow/white wire to a signal generator (such as from the microcontroller). Vary the square wave pulse width from 1-2ms and the servos are now position/ velocity controlled. A Servo is a small device that has an output shaft. This shaft can be positioned to specific angular positions by sending the servo a coded signal. As long as the coded signal exists on the input line, the servo will maintain the angular position of the shaft. As the coded signal changes, the angular position of the shaft changes. The motors are small, have built in control circuitry, and are extremely powerful for their size with high torque. There are 3 wires that connects the servo to the outside world. One is for power (+5volts), ground, and the third wire is the control wire.figure 4 shows the servo can operate 180 when given a pulse signal ranging from 600usec to 2400usec. Figure 3: Flex Sensor Works Flex sensors are analog resistors. They work as variable analog voltage dividers. Inside the flex sensor are carbon resistive elements within a thin flexible substrate. More carbon means less resistance. When the substrate is bent the sensor produces a resistance output relative to the bend radius. With a typical flex sensor, a flex of 0 degrees will give 10K resistance will a flex of 90 will give K ohms. The Bend Sensor lists resistance of K ohms. Figure 4: Servo Motor Angle 32 I J E E E S, 4(1) June 2012

5 Autonomous Motion Controlled Hand-Arm Robotic System A liquid crystal display (LCD) is a flat panel display, electronic visual display, video display that uses the light modulating properties of liquid crystals (Lcs). The LCD used here is a high quality 16 character by 2 line intelligent display module, with back lighting, works with almost any microcontroller. Each character is a 5x7 dot matrix with a cursor. It works with a 5V supply. The HD44780U dot-matrix liquid crystal display controller and driver LSI displays alphanumeric, Japanese kana characters, and symbols. It can be configured to drive a dot-matrix liquid crystal display under the control of a 4- or 8-bit microprocessor. Since all the functions such as display RAM, character generator, and liquid crystal driver, required for driving a dot-matrix liquid crystal display are internally provided on one chip, a minimal system can be interfaced with this controller/driver. A single HD44780U can display up to one 8-character line or two 8- character lines. The keyboard consists of 6 switches each intended for controlling the six servo motors. It is connected to the microcontroller. On each press on the switch the corresponding servo motor moves. Figure 5 shows the robotic arm movement. Since the arm has a few joints, it can imagine, the human arm, in addition to shoulder, elbow, and wrist, coupled with the finger joints; there are a lot of joints. The main advantage over traditional DC or AC motors is the addition of motor feedback. This feedback can be used to detect unwanted motion, or to ensure the accuracy of the commanded motion. It can attain precise control of position, velocity, and torque using servo motors. Once programmed, a robotic arm can perform the same actions over and over with unrivaled accuracy for years on end without ever breaking down. In fact, reliability, flexibility, and ease of use are the primary benefits of using a robotic arm. The most obvious advantages of a robotic arm over manual labor are that a robotic arm doesn t Figure 5: Robotic Arm Movement get sick, take vacations or get tired. Another advantage of the robotic arm is flexibility. It generally has a small footprint and mounting flexibility, so it can easily be installed in most plants. Robotic arms also provide operational flexibility. Once the robotic arm is installed in the plant, programming it is generally easy. Software supplied by the manufacturer prescribes the arm s general movements. Then, an operator walks the robot through the specific motions.once programmed, a robotic arm can perform the same actions over and over with unrivaled accuracy for years on end without ever breaking down. In fact, reliability, flexibility, and ease of use are the primary benefits of using a robotic arm. (B) Software Architecture The coding for this system is done by using Embedded C. Flow charts for the important software sections is given below. I J E E E S, 4(1) June

6 Niji Johnson and P. Sivasankar Rajamani Figure 6: Robotic Arm Lifting Object IV. CONCLUSION The paper represents a design and implementation of a robotic arm indented to use in chemical plants where it is difficult to do the work with human hand and in industries to pick the heavy weighted object which can t possible with man. It can be operated both in auto or manual mode which makes the robotic arm easier to handle. The tests prove that the designed system can satisfy its goals within the budget limits. III. RESULT To verify the working of the robotic hand-arm system it is placed on a table. Then first selected the mode of operation that is auto mode or manual mode. When auto mode selected, the robotic arm read the values from MEMS and flex sensors and for the corresponding values the motor rotated and the arm moved in one of the direction and the hand-arm lifted the chess coin in that direction. In manual mode, the keypad or switch is used in robotic arm to move in one direction and it lifted the chess coin in the particular direction. Figure 6.shows the result of a robotic arm which lifted the chess coin in a particular directionfrom the chessboard. REFERENCES [1] Takahiro Endo, Haruhisa Kawasaki, Tetsuya Mouri, Yasuhiko Ishigure, Hisayuki Shimomura, Masato Matsumura, and Kazumi Koketsu, (2011) Five- Fingered Haptic Interface Robot: HIRO III, IEEE Transactions on Haptics, 4(1). [2] Kawasaki H., Ohtuka. Y., Alhalabi. M. O. and Mouri. T. (2006), Haptic Rendering and Perception of Frictional Moment, Proc. Euro- Haptics Conference., pp [3] Maekawa. H and Hollerbach. J. (1998), Haptic Display for Object Grasping and Manipulating in Virtual Environment, Proc. IEEE International Conference. Robotics and Automation, pp [4] Magnenat-Thalmann. N. and Bonanni. U., (2006), Haptics in Virtual Reality and Multimedia, IEEE Multimedia, 13(3), [5] Ueda. Y. and Maeno. T. (2004), Development of a Mouse-Shaped Haptic Device with Multiple Finger Inputs, Proc. IEEE/RSJ International. Conference. Intelligent Robots Systems, 3, [6] Available: [7] Available: 34 I J E E E S, 4(1) June 2012