CUI Devices' incremental, absolute and commutation rotary encoders with capacitive sensing technology offer a combination of performance, reliability, and accuracy not available with traditional encoders. Featuring up to 22 programmable resolutions, an operating temperature range from -40°C up to +125°C and low current draw, AMT modular encoders provide a compelling solution for a range of applications.
Rotary encoders provide critical information about the position of motor shafts and thus also their rotational direction, velocity, and acceleration. They are vital components in the motion-control feedback loop of industrial, robotic, aerospace, energy, and automation applications. In these installations, encoders are asked to provide long-term reliability, durability, and high performance despite often working in severe conditions that include dust, dirt, grease, fluctuating temperatures, and heavy vibration. The need for encoders has been increasing dramatically with the rise in applications requiring precise motion control. However, standard encoders—including optical and magnetic—result in unnecessary tradeoffs between durability and accuracy that can now be avoided by utilizing a capacitive-based encoder.
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 (Figure 1). 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.
By design, the encoder ASIC's electrical output is 100% compatible with optical and magnetic encoders. This non-contact encoder implementation has several significant user benefits:
There is another benefit, although a less-obvious one, for designers fine tuning the proportional-integral-derivative (PID) control loop: the ability to adjust the encoder's ppr count to optimize performance without the need to change encoders. This ability to dynamically modify the resolution greatly simplifies the system optimization process, which is usually done via adjustments to the code, or by changing the encoder's line count (resolution). With an optical encoder, the latter process requires different encoders to be purchased and installed, increasing overall cost and lengthening the design cycle. With the capacitive-based encoder, the control engineer simply instructs a change in the line count parameter of the encoder until the desired control-loop result is obtained.
Even in installation and production, the capacitive encoder brings other benefits. Mechanically, its mounting holes are also matched to the other encoder types, making it a fit-and-function compatible unit (Figure 2). Thus, a single encoder can be fitted to different diameter shafts simply by using adapter sleeves, which reduces the number of SKUs in production and repair stock.
With the availability of field-tested encoders based on capacitive-sensing principles, there's no longer a need for the design engineer to make the difficult choice between the attributes that optical and magnetic encoders force: short and long-time reliability versus output accuracy. The capacitive encoder excels at both, and also brings additional benefits in mechanical mounting, inventory, ppr selection, readout zeroing, and power consumption, all with full compatibility to standard outputs.