Actuators and sensors. Part 1 презентация

Actuators and sensors. Part 1 Lecture 12 Irob 2305 Introduction to Robotics

outline Motivation, why robots need sensors? Difference between actuators and sensors Robotic sensor classification Sensor Performance Calculation of errors

Sensors in Robotics are primarily used for two different purposes: Sensors in Robotics are primarily used for two different purposes: 1. Give the robot information about itself 2. Give the robot information about its environment

Any kind of device that converts one kind of energy into another Sensors: input transducers Actuators: output transducers

Common complete robot system

classification Robot sensors can be classified into two groups: Internal sensors and external sensors Internal sensors: Obtain the information about the robot itself. – position sensor, velocity sensor, acceleration sensors, motor torque sensor, etc

External sensors External sensors: Obtain the information in the surrounding environment. – Cameras for viewing the environment – Range sensors: IR sensor, laser range finder, ultrasonic sensor, etc. – Contact and proximity sensors: Photodiode, IR detector, RFID, touch etc. – Force sensors: measuring the interaction forces with the environment, etc.

Evaluation Criteria for Sensors Evaluation Criteria for Sensors 1. Sensitivity - how sensitive is the sensor - usually max. sensitivity that provide linear accurate signals. 2. Linearity - operation is linear to the input. 3. Range - difference between max. & min. value. 4. Response time - faster than the sampling time in micro- processor. 5. Accuracy - different between measured and actual. 6. Repeatability - ability to repeat between several measuremets. 7. Resolution - a measure of the number of measurementy. 8. Type of output. 9. Physical consideration - weight and size. - reliability. - interfacing.

Device error Absolute Error (EA): EA = measured value – true value EA = Y-X Relative Error (ER): ER = |EA/X|*100% Example: X = 20 °C, Y = 21.3 °C , find ER ? EA = 21.3 – 20.0 = 1.3. ER = 1.3/20 *100 = 6.5 %.

Tolerance (Limiting Error)

Accuracy & Inaccuracy Definition: A measure of how close the output of the Instrument (measured value - Y) to the true value - X. Absolute Accuracy: Relative Accuracy:

Example: X = 20 °C, Y = 21.3 °C , find AA &AR ? Example: X = 20 °C, Y = 21.3 °C , find AA &AR ? EA = 21.3 – 20.0 = 1.3. ER = 1.3/20 *100 = 6.5 %. AA = 1-0.065 =0.935. AR = 93.5%. Inaccuracy (Uncertainty) = 1- AA. = ER/100. Note: Inaccuracy is often given as a percentage of full scale (f.s) reading of an instrument.

Analog sensor: Potentiometer Analog sensor for measuring the rotational position Potentiometer = varying resistance Resistance changes with the position of the deal Converts rotational angel (physical input) to resistance (electrical output)

Sensor response curve for potentiometer Used to define different kind of properties of sensor including errors.

Range (full scale) The difference between the minimum angle and the maximum angle

Nonlinearity error

Sensitivity The amount of change in the output -> results from a particular change in the input

Next: wide range of sensors