Rotary encoders have a critical role to play in modern motion control systems, allowing rotational movement to be tracked in real time, which enables accurate feedback data to be acquired that will ensure optimal long-term performance. Covering a broad and varied array of prospective applications, these items are now finding their way into numerous different systems – including industrial drives, factory automation equipment, robotics, etc.
 
The characteristics of such application scenarios mean that the specified encoders need to work in the most demanding environments and cope with challenging conditions day-in/day-out. They will have to contend with extreme temperatures and vibrational movement, and various other factors that can potentially impinge on their operation are commonplace. In order to mitigate these, engineers really need to look again at how they approach encoder selection and move away from conventional thinking on this subject.
 
The primary function of a rotary encoder is in relation to the control of electric motors. Brushless direct current (BLDC) motors have grown in popularity over the course of the past couple of decades, thereby enabling more compact motor systems (with much higher torque-to-weight ratios) to be installed – featuring greater energy efficiency (in line with increasingly stringent environmental guidelines), elevated speeds, enhanced reliability and reduced noise. Likewise, stepper motors apply the same principles as BLDC devices, but their motion is broken up into several different steps. These devices are able to deliver considerable torque, and can also prove to be very cost-effective. BLDC/stepper motor operation is dependent, however, on having closed-loop position control so that the power needed to drive the motor is delivered correctly. This calls for constant access to precise speed and positioning data – which is where encoders come in.
 
The more accurate the motor control is, the greater the efficiency of the system will be – leading to lower running costs, or in the case of battery-powered hardware, sustaining longer operation. Therefore, it is vital that an appropriate encoder solution is chosen. Established rotary encoder deployments will rely on one of two widely used encoding technologies. These are optical-based and magnetic-based. Each has its own distinct nuances – with certain advantages, but also considerable inadequacies that engineers will need to be aware of when they are making key design decisions. Let’s now look at both of them in more detail.