10/10/2014Jason Holm

ME 486

Encoders and Sensors

Outline

Overview

Arduino Thermostat

In Class Problem

Encoder Selection

Video

DefinitionSensor – 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 – ConcentrationpH levels, toxicity, pollutantsComponent 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 SignalsOutput 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 tempLogic based programming

List of Sensors

Pg. 124-125

Table 6.2, Page 124-125

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 ArmRotating

Shaft

Tool

1 cm

9 cm

Figure 1

Solution

Approximate as triangle

Required resolution: θ = 0.5729°

Remember:n = number of bits2n - Number of partitions -> 22 = 4 partitions 360/ 2n = angle of partition -> 360/ 22 = 90 °

Solving for n:360/ 2n = 0.57297

n = 9.295 bitsRound up to 10 bits

Double check: 360 / 210 = 0.351 ° < 0.5729°

.1 m.001 m

θ

Solution

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?

Optical Rotary Encoders

Absolute Encoders

TRD-NA1024

Number of bits

Other Considerations

Summary Sheet

Price Comparison

Light Duty TRD-MX1024-BD Medium Duty TRD-N1024-RZWD

$994 mm shaft/ 25.4 mm diameter body1024 Pulses per revolutionAxial Load – 20N, Radial Load – 30NIP50 – Dust ProofMax speed: 5000 rpmAgency approval: CE, RoHS

$27110 mm shaft/78 mm diameter body1000 Pulses per revolutionAxial Load – 50N, Radial Load – 100NIP65 –Splash ProofMax speed: 5000 rpmAgency approval: CE, RoHS

$1358 mm shaft/ 50 mm diameter body1024 Pulses per revolutionAxial Load – 30N, Radial Load – 50NIP50 – Dust ProofMax speed: 5000 rpmAgency approval: CE, RoHS

Heavy Duty TRD-GK1000-RZD Absolute Encoders TRD-NA1024-NWD

$2718 mm shaft/50 mm diameter body1024 Pulses per revolutionAxial Load – 30N, Radial Load – 50NIP65 – Splash ProofContinuous max: 3000rpm, Instant max: 5000rpmAgency 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

Video Examples

Eitel, Elisabeth. "Basics of Rotary Encoders: Overview and New Technologies." Machine Design Magazine 7 May 2014: n. pag. Web. 30 June 2014.

"Optical Encoders." Code For Free. N.p., n.d. Web. 09 Oct. 2014.

"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. 2014.

"Insight - How Computer Ball Mouse Works." Insight. N.p., n.d. Web. 09 Oct. 2014.

"Industrial and Light Industrial Sensors." MTS Sensors. N.p., n.d. Web. 09 Oct. 2014.

References