10/10/2014 Jason Holm ME 486 Encoders and Sensors

Overview Arduino Thermostat In Class Problem Encoder Selection Video

Sensor – a device that converts physical stimulus or variable of interest into a more convenient form for the purpose of measuring the stimulus. Encoder – a device used to represent the current position of arms and joints Physical Stimulus Sensors/ Encoders Output Signals

 Stimulus Types Stimulus Mechanical – Position, velocity, acceleration, rotation, torque, pressure, … Electrical – Voltage, current, charge, resistance, conductivity Thermal – heat, heat flow, specific heat, Thermal conductivity Radiation– types of radiation (gamma,..) intensity, wavelength Magnetic – Magnetic field, flux, conductivity, Permeability Chemical – Concentration pH levels, toxicity, pollutants Component identities Table 6.1, pg. 123

 Encoder Types 1.Absolute -Give information about the position of the shaft -Do not need to be “homed” when turned on 2.Relative -Provides information about motion of the shaft, which is further processed into speed, distance, position, etc. -May need to be “homed” in order to work properly EXAMPLES

 Output Signals Output Types Discrete Sensor - Produces that can only have certain values Digital Sensor - Produces digital output signal in form of parallel status bits or series of pulses Binary Sensor - Produces ON/OFF signal only Analog Sensor - Produces a continuous analog signal such as voltage Pg. 123

 Industry Trends Exploded iPhone Microsensor technologies Physical dimensions in microns Fabrication techniques similar to integrated circuit production More common Low cost More applications Easier interface

Industry trends - Arduino Thermostat Sensor type – Temperature sensor Programming – Voltage into temp Logic based programming

 List of Sensors Pg Table 6.2, Page

 Desirable Features Pg. 126 Table 6.3 High accuracy – low systemic errors High precision – Noise is low Wide operating range High speed response Ease of calibration Minimum drift – little loss of calibration over time High reliability – doesn’t breakdown, withstand diverse environments Low cost Ease of integration – programming language, signal type

 Sensor and Encoder Considerations Application – Mechanical, Thermal, Electrical, … Size – Dimension vs available space Cost Resolution – how accurate Output signal – voltage, gray code Measurement rate Range of sensing Support Life Cycle

 Example Problem A robot arm consists of a rotating shaft and an arm, welded to that shaft. There is a tool placed at the end of the arm (see Figure 1). An absolute rotary encoder, which measures angular position, is attached to the rotating shaft. If the minimum tool movement that you wish to detect is 1 mm, what bit encoder would you need? Rod length is 9 cm. Shaft diameter is 2 cm. Encoder Robot Arm Rotating Shaft Tool 1 cm 9 cm Figure 1

Approximate as triangle Required resolution: θ = ° Remember: n = number of bits 2 n - Number of partitions -> 2 2 = 4 partitions 360/ 2 n = angle of partition -> 360/ 2 2 = 90 ° Solving for n: 360/ 2 n = n = bits Round up to 10 bits Double check: 360 / 2 10 = ° < °.1 m.001 m θ

Other Considerations: Measurement rate? -> How fast will shaft be spinning? Operating environment? -> Acid resistant, water proof… Measurement Range?-> 0 ° – 360 °? Durability?-> How long will this last? Size?-> Will this fit onto robot?

 Price Comparison Light Duty TRD-MX1024-BD Medium Duty TRD-N1024-RZWD $99 4 mm shaft/ 25.4 mm diameter body 1024 Pulses per revolution Axial Load – 20N, Radial Load – 30N IP50 – Dust Proof Max speed: 5000 rpm Agency approval: CE, RoHS $ mm shaft/78 mm diameter body 1000 Pulses per revolution Axial Load – 50N, Radial Load – 100N IP65 –Splash Proof Max speed: 5000 rpm Agency approval: CE, RoHS $135 8 mm shaft/ 50 mm diameter body 1024 Pulses per revolution Axial Load – 30N, Radial Load – 50N IP50 – Dust Proof Max speed: 5000 rpm Agency approval: CE, RoHS Heavy Duty TRD-GK1000-RZD Absolute Encoders TRD-NA1024-NWD $271 8 mm shaft/50 mm diameter body 1024 Pulses per revolution Axial Load – 30N, Radial Load – 50N IP65 – Splash Proof Continuous max: 3000rpm, Instant max: 5000rpm Agency approval: CE, RoHS

 Major Vendors SENSORS Automation Direct - Various MTS Temposonics – Absolute non-contact linear position sensors ENCODERS Anaheim Automation – Rotary, Linear Encoder Renishaw – Rotary, Linear Encoders

 Eitel, Elisabeth. "Basics of Rotary Encoders: Overview and New Technologies." Machine Design Magazine 7 May 2014: n. pag. Web. 30 June  "Optical Encoders." Code For Free. N.p., n.d. Web. 09 Oct  "TRD-N1024-RZWDENCODER 1024 PPR 8mm SOLID PUSH- PULL 5-30VDC 2m (6.5ft) CBL MED DUTY." TRD-N1024-RZWD. N.p., n.d. Web. 09 Oct  "Insight - How Computer Ball Mouse Works." Insight. N.p., n.d. Web. 09 Oct  "Industrial and Light Industrial Sensors." MTS Sensors. N.p., n.d. Web. 09 Oct