Encoders
October 3, 2012
Encoders An encoder is a sensor of mechanical motion that generates digital signals in response to motion. Encoders help provide the user with information about position, velocity, and direction.
Rotary/Shaft Encoders
Types of encoders • • • •
Linear encoders Rotary encoders Absolute and incremental encoders Magnetic and optical sensor encoders
Absolute vs. Incremental • Incremental encoders are able to record changes in position. Some may need to go to a “home” position when they are initially started. • Absolute encoders are more complex in that they can be turned on and already know their position. This is due to a more complex optical sensor configuration.
Magnetic vs. Optical • Optical encoders shine a LED light through a disk that has been manufactured by imprint lithography. It uses a sensor to read the light to determine position. A magnetic encoder uses several evenly spaced N and S pole magnets and a sensor to read the change in magnetic position.
Applications • Automotive (controlling speed) • Consumer Electronics and Office Equipment (Printers and scanners) • Industrial (CNC machine control) • Military (positioning antennas) • Scientific Instruments (positioning telescopes)
Think before you buy • • • • • • •
Physical conditions (moisture, dust particles, temperature) Accuracy (absolute vs incremental) Shaft size compatibility Is it explosion proof? RoHS compliancy. What type of software will I need? SiGNUM Vendors Heidenhain, Renishaw, Netzer, and Temposonics
Price comparison Hollow Differential With Index Magnetic Rotary Encoders $590 • •
• •
Tracks 0 to 200,000 Cycles Per Second Operating Temperature of -20° to +105° C 100 to 2,560 Cycles Per Revolution (CPR) 400 to 10,240 Pulses Per Revolution (PPR)
ENC-A4PS - Optical Rotary Encoders $290 • • • • •
Miniature Size 100 to 360 Cycles per Revolution (CPR) Tracks 0 to 30,000 Cycles Per Second Off-Axis Mounting Tolerance of 0.010 Operating Temperature of -10° to +85° C
State of the art
State of the art
Question • Question: If an encoder has a resolution of 1024 and is mounted to a shaft of diameter 1”, what will be the pulses per inch and inch per pulse with this combination?
• Use these equations: PPR = resolution * 4 (PPR) / (2𝜋𝑟) = pulses per inch (r = radius of shaft) (Pulses per inch)^-1 = inch per pulse
Answer • (1024*4)/(2𝝅*.5) = 1303.79 pulses per inch (1303)^-1 = .000767 inch per pulse
References Basic knowledge of encoders: http://www.anaheimautomation.com/manuals/forms/encoder-guide.php Physical condition limitations: http://www.encoder.com/selectguide.html#environmental http://www.encoder.com/selectguide.html Price comparison: http://www.anaheimautomation.com/products/encoder/optical-incrementalrotary.php?tID=1054&pt=t&cID=422 State of the art: http://www.renishaw.com/en/new-state-of-the-art-air-bearinggantry-system-features-renishaws-high-performance-incremental-encoder--12331 Videos: http://www.youtube.com/watch?v=nLo5qJahzLs http://www.youtube.com/watch?v=_6vIRhdnwEs&feature=relmfu Technical paper: http://www.sciencedirect.com/science/article/pii/S0167931706000335
Information we should know about Basic knowledge of encoders: http://www.anaheimautomation.com/manuals/forms/encoder-guide.php Physical condition limitations: http://www.encoder.com/selectguide.html#environmental http://www.encoder.com/selectguide.html Price comparison: http://www.anaheimautomation.com/products/encoder/optical-incrementalrotary.php?tID=1054&pt=t&cID=422 State of the art: http://www.renishaw.com/en/new-state-of-the-art-air-bearinggantry-system-features-renishaws-high-performance-incremental-encoder--12331 Videos: http://www.youtube.com/watch?v=nLo5qJahzLs http://www.youtube.com/watch?v=_6vIRhdnwEs&feature=relmfu Technical paper: http://www.sciencedirect.com/science/article/pii/S0167931706000335
Consider these details • Costs of products? • How are products supported, maintained? • What is the customer base?
• How easy is it to integrate with other products/components?
• Can I exchange data with it? • What protocol does it use for networking? Or interfacing?
• What are its speed, acceleration, I/O number, response time, ... etc.? • Does it satisfy emerging standards?
• What are its capabilities, limitations, • Has it been UL tested/listed? etc.? (gray code?) • Does it have an API set for software • Mean time between failure? integration? • What programming language is it written in? • What operating system does it use? • Are their alternative technologies?
• Who are the primary vendors?
• Who is the most recognized vendor? • Where is the technology used? Why?
PPT would have been better by expanding the following detail. • Better survey on costs of products? Versus speed, resolution, application?
• Sensor speed, acceleration, response time, ... etc.? • Capabilities, limitations, etc.? (What is gray code?) • Mean time between failure (MTBF)? • How do we protect sensor against dirty or explosive environments? • How easy to integrate within other products/components?
• Protocol for networking? Interfacing? • Satisfy emerging standards? • Does it have an API set for software integration? How do you integrate? • Who are the primary vendors? Show vendor list. • Most recognized vendor? Why? • Where is technology used? Why?
