In a modern multidisciplinary engineering system, the focus of our attention is the plant or process. Sensors tell us what is happening, actuators make things happen, and the complex decision making is embedded in the real-time code executed by a computer.…
Every application of measurement, including those not yet invented, can be put into one of three categories or some combination of them: monitoring of processes and operations; control of processes and operations; and experimental engineering analysis. In real-time control applications, a process is subject to disturbances and aging, and its model parameters are not exactly known. In the open-loop system, this results in a changing and inaccurate output. However, a closed-loop system senses the change in the output and attempts to correct the output. The sensitivity of a control system to parameter variations and disturbances is of prime importance. A primary advantage of a closed-loop (feedback) control system is its ability to reduce the system’s sensitivity. As the loop gain is increased, the sensitivity of the closed-loop control system to changes in the process and controller decreases, but the sensitivity to changes in the measurement system becomes -1. In real-time, closed-loop-control applications, the measurement system must be accurate, fast, and stable.
All multidisciplinary mechatronic systems are computer controlled with sensors and actuators. Understanding the analog domain – the world of the plant, sensors, and actuators – and the digital domain – the world of the computer – along with the key issues of sampling, quantization, and aliasing is essential.
This module includes the types of applications of measurement instrumentation, the generalized configurations and functional descriptions of measuring instruments, and generalized performance characteristics of instruments. The issues in sensor selection include accuracy, repeatability / drift, sensitivity / resolution, bandwidth (speed of response ), signal-to-noise ratio (dynamic range ), and input and output impedances.
Selection, modeling, analysis, experimental verification, evaluation, and implementation of a variety of analog and digital sensors for mechatronic applications, including mechanical, electrical, electromechanical, thermal, and fluid systems, are discussed.
Electromechanical Actuators studied include brushed and brushless DC motors and the step motor. Electrohydraulic Actuators studied include the hydraulic cylinder and the hydraulic motor. A model-based actuator selection process is applied with physical and mathematical modeling and dynamic analysis of each actuator model. Trajectory planning using electronic cams is studied. Implementation power and control electronics for each actuator are discussed, as are integration issues of the actuator into the multidisciplinary engineering system.
