How do you perform the project planning for encoder systems?
The use of a specific encoder is based on the requirements of the application. Each encoder in the offered capability classes can be used in relation to the application. If the application is not very dynamic, it may be sufficient under certain circumstances to implement rapid/creep speed positioning via a low-resolution incremental encoder.
However, speed control is essential for dynamic positioning. A high encoder resolution is necessary for the speed control quality. This is why SEW-EURODRIVE recommends sin/cos encoders. The signals are scanned with an A/D converter that achieves a higher resolution than the typical 1024 (4096 due to quadruple evaluation) increments of a TTL or HTL incremental encoder.
Linear systems are often used on the track for travel distance positioning. They have the advantage of measuring directly on the track and so are independent of the slip of the drive system.
For functional safety, certified safety encoders are used to implement safety functions. They have the advantage that they are already certified as a safety-related component and can be used for the application-related and safety-relevant tasks at the same time.
The following table lists the most important characteristics of the encoder systems. For further information, refer to chapter Encoder capability class.
Encoder system | EK8S/EV8S/EK8Z Incremental encoder | EI8Z/EI8C/EK8C/EV8C/EK8R/EV8R Incremental encoder | EI71/EI72/EI76/EI7C Low-resolution incremental encoders |
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Capability class | High | Medium | Basic |
Output signal | 1024 sin/cos periods/revolution or with MOVILINK® DDI | 1024 periods/revolution (HTL/TTL level) or with MOVILINK® DDI | 1 to 24 periods/revolution |
Accuracy | < 2 angular minutes | < 7 angular minutes | < 300 angular minutes |
Maximum usable resolution | < 22 bits | < 14 bits | < 5 bits |
Use | For speed control and "incremental" positioning | For speed control and "incremental" positioning | For simple "incremental" positioning and speed monitoring |
Suitable for | Asynchronous DR.. AC motors, asynchronous DR2L servomotors. | Asynchronous DR.. AC motors, asynchronous DR2L servomotors. | Synchronous DR2C.. motors, asynchronous DR.. AC motors |
Speed control | Suitable for dynamic applications | Suitable for dynamic applications with limitations in the lower speed range | – |
Safety encoder | Optionally as a certified safety encoder for implementing safety functions (sin/cos signals or MOVILINK® DDI) | – | Optionally as a certified safety encoder for implementing safety functions (EI7C FS) |
Other characteristics | Simple startup due to electronic nameplate | Simple encoder system for standard applications For EI8R/EI8C: Motor without additional length | Motor without additional length |
Encoder system | RK8M Resolver | EK8W/AK8W/AV8W Single-turn absolute encoder (EK8W), multi-turn absolute encoder (A.8W) EK9Z/AK8Z Single-turn absolute encoder (EK9Z), multi-turn absolute encoder (AK8Z) | AK8Y/AV8Y Multi-turn absolute encoder with synchronous serial interface |
|---|---|---|---|
Capability class | Medium | High | High |
Output signal | Amplitude-modulated sin/cos signal; 2-pole |
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Accuracy | < 40 angular minutes | < 2 angular minutes | < 2 angular minutes |
Maximum usable resolution | < 16 bits | < 22 bits | < 22 bits |
Use | For speed control and determining the rotor position within one motor revolution as well as "incremental" positioning | For speed control and determining both the rotor position and absolute position | For speed control and determining both the rotor position and absolute position |
Suitable for |
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Speed control | Suitable for dynamic applications | Suitable for highly dynamic and dynamic applications | Suitable for highly dynamic and dynamic applications |
Safety encoder | – | Optionally as a certified safety encoder for implementing safety functions (sin/cos signals or MOVILINK® DDI) | Optionally as a certified safety encoder for implementing safety functions (sin/cos signals) |
Other characteristics | Mechanically and thermally very robust | Simple startup due to electronic nameplate | – |
