Sensors and Actuators Simple Sensors Switches and Pots Other Sensors Simple Actuators LEDs and Buzzers DC Motors MAE 156A

2 Mechatronics Hardware A mechatronic system may include sensors, actuators, and one or more embedded control computers. This lecture provides an overview of actuator and sensor hardware, and their interface with a typical microcontroller. Process Sensor Micro- Controlle r OperatorActuator

MAE 156A 3 Simple Sensor : Switch A switch is a simple sensor that yields a binary (on/off) response. micro SW When the switch (SW) is open, the microcontroller will see 0 volts (logical false). When SW is closed, the microcontroller will see 5 volts (logical true). The value of R2 is set so that only a small current flows from the microcontroller. This current is approximately given by, The resistor R1 is not really needed; however, it can be added to protect the micrcontroller in case your evil lab partner connects the SW terminals to something other than +5 volts or ground. GND

MAE 156A 4 Simple Sensor : Potentiometer A potentiometer can be used to measure angular displacement. micro The variable y represents the position of the pot's rotating spindle; its normalized value ranges from 0 to 1. Kirchoff and Ohm's laws provide the following relationships: Assume current into microcontroller is small,

MAE 156A 5 Potentiometer Resistance The potentiometer resistance should be chosen based on current and power. micro If current through the pot is limited to a small number, say 1 mA, the pot resistance should be: The power dissipated by the pot is thus,

MAE 156A 6 Signal Conditioning The interface between a sensing device and a microcontroller may require additional signal conditioning elements. There are many “smart” sensors entering the market that include all signal conditioning elements within the sensor housing itself. Output of the sensor could be asynchronous or synchronous serial data. Low-Pass Filter TransducerAmplifier Sample and Hold Micro- Controller A/D Converter Sensor Pick-Up

MAE 156A 7 Displacement Sensors Isermann, R., Mechatronic Systems : Fundamentals, Springer Resistive Sensor Inductive Sensor Capacitive Sensor Strain GaugeEncoderIncremental Sensor Hall Effect Sensor

MAE 156A 8 Velocity Sensors Isermann, R., Mechatronic Systems : Fundamentals, Springer Translational Velocity Sensor DC GeneratorAC Generator Incremental Velocity Sensor

MAE 156A 9 Acceleration Sensors Isermann, R., Mechatronic Systems : Fundamentals, Springer Piezoelectric Acceleration Sensor Accceleration Sensor with Seismic Mass Vibration Sensor with Seismic Mass Angular Vibration Sensor

MAE 156A 10 Force, Torque, and Pressure Sensors Isermann, R., Mechatronic Systems : Fundamentals, Springer Piezoelectric Force Sensor Torque Measurement Using Strain Gauges Force Spring Deflection Sensor Pressure Diaphragm Sensor

MAE 156A 11 Simple Actuator : LED A Light-Emitting Diode (LED) is a simple actuator. It does not move anything, but its response could trigger something else to happen. micro When the microcontroller pin is set as an output, writing a logical high value puts 5 V on the output pin. The voltage drop across the LED is nearly constant. Red or green LED => 2 V Blue or white LED => 3 V Be careful that the current flow matches the specification of both the LED and the microcontroller. LED GND

MAE 156A 12 Simple Actuator : Buzzer The following circuit shows how a transistor can be used to activate a buzzer. The 2N2222 is a Bipolar Junction Transistor (BJT) that acts as a switch to activate the buzzer. Other devices, which require higher than 5 V source, can be activated in a similar way micro GND Buzzer 2N2222 Transistor E B C

MAE 156A 13 DC Motors Many actuation devices depend upon Direct Current (DC) motors. Armature Circuit: Back Electromotive Force: + roto r +

MAE 156A 14 Motor Torque The torque developed by the motor is related to the armature current. If the motor is operating in a steady-state, then the armature current is constant. The armature becomes:

MAE 156A 15 Motor Model Parameters The steady-state motor equation yields the motor's torque-speed curve. “No load speed” occurs when motor torque is zero. Motor Torque Motor Shaft Speed Linear torque- speed curve “Stall torque” occurs when motor speed is zero. Stall torque No load speed

MAE 156A 16 Further Reading Isermann, R., Mechatronic Systems : Fundamentals, Springer Bishop, R.H., The Mechatronics Handbook, CRC Press