Encoders are everywhere — and are vital in industrial, aerospace, energy, automotive and robotic applications. Operation in all of these applications will potentially have to take place in severe conditions, so when you are thinking about building a robot that can be used to mine for water on Mars, how do you decide on the best components to use? If there is a constant trade off between durability and precision, then what is the solution?
Proliferation of encoders
The latest Research and Markets report predicts that the industrial robotics market in North America is set to grow at a CAGR of 12.26% over the period 2015-2019, and with vendors using advanced technologies to develop independent robotics systems in order to remain competitive in the market, encoders are as important as ever.
Rotary encoders provide critical information about the position of motor shafts and with it their rotational direction, velocity and acceleration. With the emergence of affordable, agile, mobile robotics applications in an ever-expanding industrial and domestic setting comes the need for new techniques and solutions in rotary-position encoding. They are vital components in the motion-control feedback loop of industrial, robotic, aerospace, energy and automation applications.
Mitigating the encoder tech trade-off
Today, the most commonly used encoder technologies are the optical and magnetic types, but the challenge for design engineers has been in choosing between the trade-offs of the two. The optical approach offers the best accuracy, but with reduced reliability due to the fragility of its optical disk. The magnetic approach, on the other hand, provides greater durability, but with less accuracy, especially as temperature increases within the application.
Remember the Vernier caliper? There are countless instances where looking to the history of technology can provide an idea for something new today. The Vernier caliper, developed over 30 years ago, has provided the inspiration for a new type of encoder that offers an accurate, precise and rugged solution for today’s applications.
Capacitive sensing is commonly used for touch switches, where the user’s finger acts as the second plate of a capacitor. Touch switches are known for their resistance to dirt, water, and overall abuse, since they have no moving internal parts. However, the uses of capacitive sensing go beyond such basic on/off switches, with the ubiquitous digital caliper as a mass-market example.
When applied to encoders, capacitive sensing uses patterns of bars or lines, with one set on the fixed element and the other set on the moving element, to form a variable capacitor configured as a transmitter/receiver pairing. As the encoder rotates, an application specific integrated circuit (ASIC) counts the line changes and also interpolates to find the precise position of the encoder and direction of rotation.
Most durable and reliable encoder
Design engineers no longer need to make the difficult choice between the attributes that optical and magnetic encoders force: short and long-term reliability versus output accuracy. The capacitive encoder is able to deliver the durability of a magnetic encoder and the accuracy of an optical in one package. The AMT encoder series developed by CUI Inc. is tried and tested in a range of extreme conditions.
Past installations have included a manufacturer of baking automation equipment who consistently had issues at customer sites with flour dust and other contaminants affecting the optical encoder on a key production unit. This frequently led to line-down situations in order to replace and re-zero the encoder. By swapping the optical encoder for a capacitive one, the problem disappeared. In another case, a manufacturer of off-shore drilling equipment required that the entire motor assembly be submerged in oil due to the high pressures associated with the application. A capacitive encoder was selected because of its ability to operate without interruption in nonconductive fluids such as oil.
In fact, the AMT is put through its paces in the most severe environments— whether surveying crops, automating a factory process, or preparing to mine for water on Mars.
Filed Under: Motion Control Tips, Encoders • optical, Encoders (rotary) + resolvers
