What Is a Multi-Turn Absolute Rotary Encoder?

For standard rotary servo motors, a position feedback device is usually mounted in the rear of the motor and coupled to the rotor shaft. As the shaft spins, the device measures its position relative to the stationary stator/housing. This position information is sent to the servo drive, which compares it against the commanded position and continuously corrects for any errors. This is known as a closed-loop system.

Various sensing technologies are available, including capacitive, inductive and optical devices. Each sensing type has its own pros and cons based on cost, size, performance, ruggedness and operating temperature. While not recommended for conditions of extreme shock, temperatures or dust, optical sensors are the best choice for the majority of applications where extreme precision and responsiveness of motion make the difference for the quality and productivity of industrial processes.

SFD-M versus other high-resolution, multi-turn absolute rotary encoders. The SFD-M is comparable in performance to other encoders in its class, but is offered as an integral feature of Kollmorgen motors at a much greater value. In fact, you can save hundreds of dollars per axis, and thousands of dollars in a multi-axis machine, by choosing SFD-M.

SFD-M versus encoders with functional safety capabilities. Some position feedback devices incorporate third party-certified functional safety features, useful when it’s important to allow operators to physically interact with the machine without shutting down. The SFD-M does not offer this, so a device like the BiSS capacitive safety or EnDat inductive safety device might be a better choice for implementing functional safety features. However be aware that the cost of these devices is considerably higher, and they require the motor to be longer.

SFD-M versus the highest-resolution feedback devices. When there is a mechanical linkage between motor and load, such as a pulley, gear box, coupler or lead screw, compliance and backlash are likely to introduce errors far greater than the accuracy of the SFD-M. In these cases, and in many direct drive applications, the SFD-M enables exceptionally high-quality motion. However in direct drive applications where the highest possible position accuracy is required, an EnDat optical or BiSS optical encoder may be a better choice. These are higher in cost and require a longer motor than the SFD-M.

When not using a Kollmorgen drive. Choose a feedback device that is compatible with your drive.