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Views: 0 Author: Site Editor Publish Time: 2026-08-30 Origin: Site
(一）. Core Application Scenarios
1. Servo Oil Pump Motor (the most important application)
Injection Molding Machine Servo Energy-Saving System: The servo motor drives a fixed-quantity oil pump, delivering flow and pressure to complete all the process actions like mold clamping, injection, pressure holding, plasticizing, mold opening, and ejection.
Rotor position detection: Provides the servo driver with the rotor pole angle of the permanent magnet synchronous motor to achieve FOC (field-oriented control), ensuring motor startup, high torque at low speeds, and preventing missed steps or jitter.
Speed closed-loop feedback: Collects the motor speed in real-time and feeds it back to the driver, forming a pressure-speed dual closed loop together with the pressure sensor. The controller outputs flow commands, the resolver feeds back the speed, and the pump output is adjusted, achieving precise control of injection speed and gel speed, enabling energy-saving control of the injection molding machine.
Workflow: The injection molding machine’s main controller sends pressure and flow commands → the servo driver drives the pump motor → the resolver collects rotor angle and speed and feeds it back to the driver → the motor output is corrected in real time to match the pressure and flow requirements of each injection molding process.
Injection molding machines use semi-closed loop control: a resolver measures the motor speed, and the pump speed determines the hydraulic flow, which indirectly controls the injection and melting speed rather than directly measuring the screw displacement; the screw displacement is detected by a tie rod electronic ruler.
Electric turret / auxiliary motor for fully electric injection molding machine
Some models of fully electric injection molding machines use servo motors for injection, melt, and clamping, and may also be equipped with a rotary transformer.
These measure the absolute angle and speed of the motor rotor; they can handle frequent start-stop shocks and high temperatures, making them suitable for 24-hour continuous production.
Fully electric injection molding machines mostly use absolute optical encoders, while rotary transformers are more often used in harsh working conditions and high-vibration, large-tonnage machines.
（二）Hardware Components of the Rotary Transformer in the Injection Molding Machine System
1. Rotary transformer body: Installed at the non-output end of the servo motor shaft, the rotor rotates with the motor shaft, and the stator is fixed to the motor's rear cover; outputs SIN/COS analog sine and cosine signals, with no circuit board inside the motor, and is resistant to high temperature and vibration.
2. Resolver decoding chip (RDC): Integrated into the servo drive PG feedback card; converts the resolver's sine and cosine analog signals into digital signals for rotor angle and speed for the DSP drive.
3. Wiring: 6 cables in total — 2 for excitation (EXC), 2 for SIN, and 2 for COS differential signals; anti-interference, keep wiring away from high-current power lines.
（三）. Why servo pumps on injection molding machines prefer using resolver over optical encoders
Comparison Items | Resolver | Optical Incremental Encoder |
Structure | Pure electromagnetic coil, no optoelectronic parts, no glass encoder wheel | Light-emitting tube, receiving tube, glass code disk |
Temperature Resistance | ‑40℃~155℃, good tolerance for high-temperature motors | Generally -20~85°C, high temperatures can cause aging and failure |
Vibration and Impact Resistance | Very strong, suitable for frequent start-stop impacts on injection molding machines | Strong vibrations can easily break the code disk or lose pulses |
Environmental Resistance | Oil and dust resistant, not afraid of oil mist | Oil mist and dust can contaminate the optical path, leading to frequent malfunctions |
Electromagnetic Interference Resistance | Strong, differential analog signal | Pulse signals are easily interfered with by inverters, causing missed pulses |
Resolution | Driver decoding can reach 4096‑10000 P/R | Can achieve very high resolution |
Drawbacks | Requires a dedicated RDC decoding chip; it's a single-turn signal, losing position count when powered off, and needs magnetic pole detection when powered on | Short lifespan in high-temperature and oily environments |
(四）.Typical Injection Molding Machine Malfunctions (Related to Resolver)
1. Servo motor shakes, makes unusual noises, weak at startup;
2. Injection molding machine reports servo error, pole detection fails;
3. Injection speed is unstable, melt rotation speed fluctuates;
4. Motor sometimes works fine, sometimes gives errors;
Common causes: loose resolver wiring, damaged cables; abnormal eccentric gap in resolver stator-rotor assembly; damaged resolver body; driver RDC decoding circuit failure. During inspection, measure the resistance of the excitation, SIN, and COS coils to check condition.
