Encoders and Sensors Oct. 5, 2009 By: Kyle Dallon
What are encoders? • An encoder is a device, circuit, transducer, software program, algorithm or person that converts information from one format, or code to another, for the purposes of standardization, speed, secrecy, security, or saving space by shrinking size. • Converts a physical motion into a digital signal.
What are encoders used for? • Tracking position and movement • In creating feed back loop to control robots • Controlling other automated systems • Instrumentation devices
Types of Encoders - Linear • Typically travel along a rail, or the rail travels through the encoder. • Typically operate within 0-70°C. • Speed of travel depends on size, but many could travel between 2-2.5 m/s.
Types of Encoders - Rotary • Typically shaft or hollow shaft • Housing diameters from 1.5 to 3.25” very common • Typical frequency response up to 100Khz • Can find modular
Types of Encoders - Incremental • Can get incremental coders for just about any type of encoder. • Have outputs that repeat over a full range of motion. • Can still be very accurate.
Types of Encoders - Absolute • Can get incremental coders for just about any type of encoder. • Have a unique value for each position. • Are very accurate.
Types of Encoders - Optical • Can have either absolute or incremental. • Rotary or linear. • Not good in dirty environments. • Not good with vibrations.
Types of Encoders - Magnetic • Linear , rotary or ring. • Dirty environment and vibrations not as big an issue.
Issues to Consider with Encoders • Response time • Operation temperature • Environmental conditions • Accuracy • Resolution • Ease of movement (torque)
Vendors Costs starting at about $100 and increasing from there to thousands of dollars • Heidenhain • Automation Direct • Stegman • Encoder Products Company • Renco • Renisha • Autonics
What are sensors? • Any device that receives a signal or stimulus (as heat or pressure or light or motion etc.) and responds to it in a distinctive manner.
Where sensors are used? • Security Systems • Robots • Camera’s • Instrumentations • Appliances • Vehicles • Etc…
Types of Sensors - IR Can detect infrared light. Mouse Motion Sensor Automatic Trash Can
Types of Sensors - Ultrasonic Generate high frequency sound waves and evaluate the echo which is received by the sensor.
Other Types of Sensors • Thermal • Resistive • Force/Pressure • Many others Force Speed measured with resistance sensors
Issues to Consider with Sensors • If sensor influence the measured properties • Accuracy of sensor • Sensitive to more then one property (noise) • Response time
Example What type of sensors might you use to help you perform auto focusing for a camera? What kinds of issues would you have to deal with using these sensors? • Used Methods: • Active focusing (IR) • Passive focusing (CCD, CMOSS)
References: • http://en.wikipedia.org/wiki/Encoders • http://wordnetweb.princeton.edu/perl/webwn?s=sensor&sub=Search+WordNet&o2=&o0=1&o7=&o5=&o1=1&o6=&o4=&o3=&h=0 • http://www.epiloglaser.com/legend_linearencoders.htm • http://www.microesys.com/drcEncoders/data.html • http://www.gurley.com/Encoders/Gurley03.jpg • http://www.patchn.com/index.php?option=com_content&task=view&id=48&Itemid=74 • http://www.discountgage.com/mmGAUGES/Images/543-452Bsquare.gif • http://www.go.ednet.ns.ca/~larry/astro/telescop/encoder1.gif • http://www.motioncontrol.com/index.cfm/Optical-Encoder/
References Continued: • http://www.plantautomation-technology.com/contractor_images/elap/elap-linear-rotary.jpg • http://www.renishaw.co.in/media/img/gen/bd0bc36fe89f474293d526744bd1e8f0.jpg • http://www.raylux.ir/images/image/products/More/ST280A/ST280A_F/SL28_clip_image002.jpg • http://www.traderscity.com/board/userpix22/16139-intelligent-motion-infrared-sensor-stainless-steel-bin-trashcan-garbage-rubbish-recycling-bins-1.jpg • http://en.wikipedia.org/wiki/Ultrasonic_sensor • http://www.euclidres.com/motionSensors/ultra.gif