SARE (Smart Absolute Rotary Encoder)

thingiverse

You Need to Determine an Angle for a Mechanism in Rotation? It's Easy to Find a Sensor That Does This Function Quickly and Cheaper, But These Products Give Relative Position. However, In Some Applications, You Need to Measure an Absolute Position for an Object in Rotation. But This Kind of Sensors (Absolute Rotary Encoder) Are Expensive and Due to High Precision Mechanism, It Is Difficult to Integrate. Based on Gray Code (a Reflected Binary Code), These Sensors Use a Disc Containing Several Tracks Coded in Gray Code with an Optical Bloc to Detect the Current Position. I Propose You, With This Project, to Design Your Own Absolute Rotary Encoder with Your Favorite 3D Printer. To Begin... It's Necessary to Determine Your Need in Angle Precision, You Want Lot of Angle Precision? More Tracks Are Necessary in Your Disc! But Draw Manually Any Disc with a Gray Code of 4 and More Is Completely Crazy!! To Help You, I Wrote a Blender Python Script to Generate a Custom Disc with Any Number of Tracks. Warning! Generate a Disc with Lot Tracks Need Several Minutes of Processing... or a Good Computer! Download This Script: gray_generation.py. By Default, the Script Generate a Gray Disc of 4 Tracks. To Change This, Open the Script and Change the Value of "trackCount" (end of the script)... gray.makeGray(trackCount = 4, startDistance = 1, distance = 0.4) Project: SARE Sensor (Smart Absolute Rotary Encoder) We Need to Determine a Absolute Angle, But Why Use a Reflected Binary Code? This Is Simple, a Natural Binary Code Is Not Adapted to Detect a Change When Applied to Real Physical Mechanism, Indeed More Than One Bit Can Differ During a State Transition and There Is an Important Risk to Probe an Transitional State (wrong state). In Pratice, an Emitter Produces an IR Light, This Light Is (or not) Masked by this Associated Track and an IR Receiver Detect this State to Generate a Logical Binary State. With Several Tracks, We Can Determine the Current Disc Position. To Illustrate an Interesting Use for This Kind of Sensor, I Chose to Design a Wind Direction Sensor. It Is Designed with a Disc of 4 Tracks to Have 16 Positions, We Obtain 22.5° of Precision for the Wind Direction. Objectives Learn the Natural Binary Code and Discover an Other Binary Code: the Reflected. Learn to Use a 3D Printer to Create a Sensor Composed of Several Parts. Learn to Use Infrared LED Emitters En Receivers. Audiences Due to the Complexity of Understanding the Interest to Use the Reflected Binary Code and to Print All Parts of This Sensor, This Project Is (I Think) Adapted to 14-15 Years Old Students. Subjects Computer Science Mecanic Optics Geometry Engineering Electronics Skills Learned (Standards) Computer Science: The Binary Code Mecanic: Multi-parts Assembly and Different Types of Mechanical Linking. Optics: Using of Infrared Light. Geometry: Apply a Gray Code to a Disc. Engineering: The Interest of Relative or Absolute Rotary Sensor. Electronics: Determine the Current Angle with an Arduino. Duration Explain the Natural/Reflected Binary Code: 2 Hours. Generate Gray Disc: Depending on the Number of Tracks (1 Minute - 1 Hour). Prepare All Parts of Wind Sensor: 4 Hours. Printing: 7-8 Hours. Assemble the Wind Sensor: 1 Hour. Connect Emitters/Receivers to an Arduino and Write a Program: 4 Hours. Preparation Material: Computer with Blender Software. 4 Infrared LEDs Emitters (in 3 mm) with 4 Supports. 4 Infrared Receivers (in 3 mm) with 4 Supports). Electric Wire. An Arduino. Knowledges: Some Bases in Geometry and Mechanical. References Wikipedia - Binary Number. Wikipedia - Gray Code. Wikipedia - Wind Direction. Wikipedia - Infrared. Wikipedia - Arduino. Design and Assembly General Principle Middle Support (for Infrared Receivers) Bottom Support (for General Structure) Assembly: Middle Support Inserted in the Bottom Support and Add the Bottom Axis Assembly: How the Disc Is Fixed by 2 Axes Top Support (Emitters Support + Collimating) Add Emitters LED Supports, LED, Collimating Plate, Top Axis