SELF STABILIZING PLATFORM

Transcription

1 SELF STABILIZING PLATFORM Shalaka Turalkar 1, Omkar Padvekar 2, Nikhil Chavan 3, Pritam Sawant 4 and Project Guide: Mr Prathamesh Indulkar 5. 1,2,3,4,5 Department of Electronics and Telecommunication, Vidyalankar Institue of Technology, Wadala, Mumbai, Maharashtra. Abstract This paper presents a development of selfbalancing platform mechanism using ATMEGA microcontroller. The platform has been designed using stabilizing mechanism including Inertial measurement unit (IMU) and two servos, and controlled by an open source microcontroller. In this project the ATMEGA- 328 microcontroller, servos, and a two-degree of freedom (axis) accelerometer have been used to create the controlled platform. The controller has been designed to maintain the platform at an initially selected angle when the support structure orientation changes. The software has been written with logic to convert the digital data from the accelerometer to an acceleration magnitude vector. The magnitude is then compared to a predetermined mathematical function to infer the angle of tilt of the platform. The angle of tilt is then converted to angle of rotation for the servos to act on. Index Terms Accelerometer, IMU unit, Microcontroller, Pan Tilt, Self balancing platform, Servo motor. I. INTRODUCTION In our day to day life many more micro-electronics components exist with the very good equipment quality and performances. In this area, one is Micro electro-mechanical systems (MEMS) sensors and devices [2]. The components and devices required complete this is of cheap in cost, low energy and light in weight. In this paper sensors and other devices used are ADXL-345[1, 2, 8], servo motors [3, 4] and ATMEGA-328P [5] controller. This is widely required in products from small handheld cameras up to the defence helicopters, aircrafts and medical devices while performing precise surgeries. This paper describes easy implementation of self-balanced platform with standard part available. This is the basic concept use in auto pilot mode in aero plane. In this airplane balances itself in air without help of pilot and try to remain parallel with respect to ground level. In self-balancing platform the main components are position sensors, microcontroller and dc motor. In the implementation, we met also some problems that have been solved. One of the major applications of stabilizing platform is in self-levelling equipment like anti-motion sickness chairs [7] which causes vomiting to the travellers. II. PURPOSE The motive of the paper is to enhance the understanding of digital control devices and how it can be used to balance a platform. Also this paper is useful to analyse how close loop systems can be used along with accelerometers and gyroscope sensors to stabilize the platform. In this paper stabilization will be accomplished by using ATMEGA-328P microcontroller and an IMU unit (an accelerometer sensor) which gives feedback to two servo-motors. The purpose is also to study how the system reacts to both a symmetrically and an asymmetrically placed objects on platform. To simplify the theoretical model is considered with object is placed on the middle of the platform and tested. III. BLOCK DIAGRAM A self-stabilizing platform usually takes in account at least two angles; roll and pitch [6]. The purpose of IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 220

2 such a platform is to maintain close-to zero degrees of angle towards the direction of gravity, in other words, to stay horizontal. In order to achieve this each angle has to be measured. This can be done in a number of ways. A rotary encoder can be used to measure the rotation of the motor shaft and have the motor adjust accordingly. Another option is to use a device capable of measuring the platforms current angle, such as a gyroscope and accelerometer combination. This also enables the system to cope with the mounting (base) platform being tilted, unlike the encoder solution which can only adjust when the motor is rotated. An IMU of the scale used for this project often consists of a combination of three accelerometers and three gyroscopes placed orthogonally to each other, representing a coordinate system. An accelerometer measures G-forces, or inertial acceleration. The accelerometer is a sensor that measures acceleration in a predefined axis. The sensor can provide a reference point to determine which way is up versus down orientation. A gyroscope measures its rotational position in relation to an arbitrarily chosen coordinate system. A gyroscope will have an accumulating error and can as such often not be used alone while an accelerometer has a problem with the gravity component. These two are fortunately easily combined and will compensate each other weaknesses very well. The servo circuitry is built right inside the motor unit and has a positional shaft, which usually is fitted with a gear. The motor is controlled with an electric signal which determines the amount of movement of the shaft. Servos are controlled by sending an electrical pulse of variable width, or pulse width modulation (PWM), through the control wire. The PWM signal is a pulse of ones and zeros allowing the voltage to be set to a percentage of the maximum output voltage of the used channel. A PWM signal is usually between 0 and 255, where 0 is 0% of the available output voltage and 255 is 100%. Over a pulse, a signal of 127 will result in the signal sent being one for half of the period, and zero for the rest. This will be interpreted by the motor as a voltage of half the maximum voltage. There is a minimum pulse, a maximum pulse, and a repetition rate. A servo motor can usually only turn 90 in either direction for a total of 180 movement. The motor's neutral position is defined as the position where the servo has the same amount of potential rotation in the both the clockwise or counter-clockwise direction. The PWM sent to the motor determines position of the shaft, and based on the duration of the pulse sent via the control wire; the rotor will turn to the desired position. The servo motor expects to see a pulse every 20 milliseconds and the length of the pulse will determine how far the motor turns. The movement of servo is decided from PWM signal as follows. For example, a 1.5ms pulse will make the motor turn to the 90 position. Shorter than 1.5ms moves it in the counter clockwise direction toward the 0 position, and any longer than 1.5ms will turn the servo in a clockwise direction toward the 180 position. Depending upon the amount of change in position of Platform and direction controller energies respective motor to bring platform back to is originally/ stable position. Two dc motor are attached to platform one from top end and other from bottom with help of string such that it is parallel with respect to ground level. IV. FLOW CHART In this the digital signal processing takes in the output from the accelerometer and outputs a PWM signal to the RC servomotors. The first portion of the code initializes the processors and variables for use. Then, the code enters an infinite while loop to continually execute the code. Then the analog value tilt angle X and Y are converted into digital values and further this digital values are converted into X and Y degrees, respectively. Then, the PWM pulse width is calculated using the X and Y degrees. In this closed loop version, the PWM widths of X and Y are increased or decreased depending on the tilt degrees until the tilt degrees for X and Y are reporting a zero degree inclination. The RC servomotor controlling the X and Y axis has a PWM width determined by a simple linear relationship with respect to the inclination. Once the PWM width is determined (in ms), we scale it to our PWM period and then set those PWM values. Once the PWM signal is set, the code returns to the top of the IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 221

3 loop and repeats the block of code again. A programming flowchart is shown in figure 1. START V. RESULT In this project, we got the output as stabilized platform as shown in figure (a). Means for any movement of the movable platform the main INITIALIZE ALL VARIABLES ASSIGN ALL HARDWARE PINS CONVERT ANALOG DATA INTO DIGITAL DATA READ ACCELEROMETER VALUE CHANGE DIGITAL DATA INTO ACCELERATION Figure (a) Normal position Platform remains parallel to the earth surface as shown in figure (a). As shown in figure (a) accelerometer is mounted on the wooden base which will act as a base platform, middle square is use for horizontal levelling and inner square will use for vertical movement. In this, if we move the base platform towards the north side then the inner platform (vertically adjustable platform) will move in opposite direction that means it will move towards the south. From this we can say that movement of the movable platform is inversely proportional to the base platform. CONVERT ACCELERATION INTO TILT CHANGE TILT INTO SERVO ANGLE Figure (b) vertically stabilized. CONVERT SERVO ANGLE INTO PWM PULSE In the figure (b) the platform is stabilized horizontally. Means after moving the outer platform towards west the middle platform moves towards east and get stabilized. SEND PWM PULSES TO SERVOS Figure (1). Figure (1). Figure (1) IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 222

4 SCOPE OF PROJECT a) Precise medical surgeries. This is very useful in ships for medical operations precisely by keeping to patients stable. Same can be used in ambulances. Figure (c) horizontally stabilized In the figure (c) we move base platform towards west then according to the signal to the motor it will move towards the east. Figure (d) horizontally and vertically stabilized. In this we move this in direction other than the primary directions (East, West, North, and South). Due to this both the inner platforms will move in the opposite direction in which base platform is move. And we get the stable platform. From all above figures, we can say that, the movement of the inner platform and base platform is totally opposite. Both the inner platform is adjusted to the appropriate direction with respect to the movement of base platform to keep the inner platforms parallel to the earth surface. VI. CONCLUSION Our project is capable to stabilize the movable platform at a constant position. That means this platform will remain parallel to the earth surface. This can be used in many applications like Ships, Vehicles, Ambulance, Camera for entertainment and safety purpose. b) Aircrafts stabilizer. An aircraft stabilizer is an aerodynamic surface, it includes one or more movable control surfaces, that provides longitudinal (pitch) and directional (yaw) stability and control. A stabilizer can feature a fixed or adjustable structure on which any movable control surfaces are hinged, or it can itself be a fully movable surface such as a stabiliser. c) Antenna stabilizer. This is use where the antennas are placed at high heights, which get affect because of wind. Due to this communication can be break, so antenna stabilizer helps to keep antenna at a unique position and communication will take place without any problem. d) Camera stabilizing. Self-stabilization can be used to stable the cameras in films and in photography. e) Stabilizing platform in vehicles to prevent motion sickness. In this the sheets can be place on a single platform and this platform can be stabilized using this concept, due to which motion sickness problem can be solve. REFERENCE [1] IMUSENSORhttps:// blication/ _study_of_inertial_meas urement_unit_sensor [2] MEMSregistermaphttp://invensense.com/mem s/gyro/documents/rmmpu6000a.pdf( ) [3] Servomotorhttp:// 2/TEXT/NTRAK2002/ pdf [4] Servomotorhttp://robokits.co.in/motors/microservo-9g [5] ATMEGA328phttp:// Atmel427358bitAVRMicrocontrollerATmega P_Datasheet.pdf [6] Anglescontrolledbyservohttp://howthingsfly.si.edu/flight-dynamics/roll-pitch-and-yaw [7] Antimotionsicknesshttp:// atents/us IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 223

5 [8] elerometers/adxl345.html#productdocumentat ion IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 224