International Conference on Sustainable Built Environment NANCO AND UNIVERSITY OF MELBOURNE JOINT RESEARCH SESSION ON NANOTECHNOLOGY AND SUSTAINABLE BUILT ENVIRONMENT December, 2010 at Earls Regency, Kandy, Sri Lanka

MOTION SENSOR APPLICATIONS IN SMART BUILDINGS

Motion detection and control of (smart) buildings is important to ensure the safety of its 1. Occupants 2. Equipment being used and To ensure long lasting of the building itself. Vibrations due to nearby vehicles on highways, trains on railways, etc., can be detected using Si based ACCELEROMETERS attached to the building. Such feedback can be used to maintain vibration free platforms inside (smart) buildings. Abstract

Objectives & methodology To compensate the vibrations in buildings using a combination of active and passive compensators. Design is simulated with the required models of controllers, spring damped platforms and the actuators using typical vibration signals in building environments.

MEMS Accelerometer Designed with a small proof mass suspended by a spring and a damper system. Mass is free to move within a certain limit. Capacitors are used to measure the displacement of the spring suspended proof mass of the accelerometer

MEMS Accelerometer contd., Capacitance is inversely promotional to the gap (d) in between the two plates. The change of capacitance is measured by the voltage ratio between the two series capacitors (C 1 and C 2 ). Acceleration of the proof mass (a) is connected with the displacement (d) according to: k is spring constant

Vibration free platform Two accelerometers used at – Spring-mass damper – vibration free platform The spring-mass damper smooth out the vibrations The controller drives the linear actuator to compensate the damped oscillations of the spring damped platform.

Spring-Mass Damper Design Active compensator is mounted on a spring-mass damper. Spring-mass damping system is used to smooth out the vibrations.

Parameters of the spring-mass damper are selected to have the following Input – Output relationship Spring-Mass Damper Design

Active Compensator Active compensator compensates the vibration inputs of the accelerometer 01 placed on the spring- mass damped platform. Any uncompensated vibrations picked by the second accelerometer placed on the vibration free platform. Output of the second accelerometer is inverted and fed to the actuator system as a disturbance input.

Active Compensator

Actuator Model The actuator consists of a dc motor and a rotationl – linear motion converter. Linear motion of the vibration free platform and the rotational motion of the DC motor is linearly proposional to each other.

Actuator Model

Results Motion profile of the vibration free platform is compared with the output of the accelerometer 01 to evaluate the performance of the system.

Results The system is further evaluated using the compensation error generated at the second accelerometer placed on the vibration free platform.

Conclusion Vibration input to the system and the inverted acceleration of the corresponding control action is plotted on the same graph to analyse the system in a more discriptive manner.

Concluion Time delay of the system model is the main reason for the compensation error and which will be different on the real system.

Thank You