Resolver
Why use a resolver instead of an encoder on a CNC motor?
Resolvers provide robust analog position feedback in dirty, hot, or high-vibration environments where optical encoders are more vulnerable to contamination and mechanical damage. They are often preferred for heavy-duty machine tools and industrial automation.
What is the resolver’s electrical principle?
It works as a rotary transformer: an energized primary induces voltages in two secondary windings that are phase-shifted by 90°. The amplitude relationship of the sine and cosine outputs is used to compute the rotor's absolute angular position.
What failure symptom usually appears first?
Common early symptoms are unstable speed feedback, servo following errors, loss of commutation, or inability to establish a valid home/reference position when the drive cannot interpret the angle signal correctly.
A resolver in CNC manufacturing is a rotary position sensor that converts shaft angle into analog sine/cosine electrical signals. It provides absolute angular feedback for motors, spindles, and servo axes, tolerating harsh conditions like coolant, vibration, and contamination better than optical encoders.
On CNC mills, lathes, and routers, resolvers are mounted on motor shafts or coupled to them to provide rotor position and speed feedback without relying on delicate optical disks. The sensor's two secondary windings are displaced by 90°, producing sine and cosine outputs that the drive uses to calculate absolute angular position from the phase relationship. This matters in real-world shop floors because resolvers withstand oil mist, coolant splash, chips, and vibration that would cripple optical encoders. They are standard in servo-axis feedback, spindle commutation, and heavy-duty automation cells where reliability under harsh conditions is critical. Machinists trust resolvers for consistent closed-loop motion control, knowing that electrical noise or mechanical misalignment are the main threats to performance, not the sensor's rugged design itself.
Miswired sine/cosine leads: Swapping excitation or secondary connections causes the drive to read the wrong angle, leading to servo hunting, following errors, or failure to find home position. Proper verification of wiring is essential during replacement.
Incorrect mechanical phasing or coupling: Mounting the resolver with the wrong angular relationship to the rotor introduces an offset, resulting in poor commutation, unstable torque, or misindexing of the axis. Mechanical alignment directly impacts feedback accuracy.
Ignoring signal integrity in a noisy enclosure: Damaged cables, poor shielding, coolant intrusion, or loose connectors distort the low-level AC feedback signals, producing jittery position data and intermittent faults. Connection quality and shielding are critical in such environments.