Pertaining to open-loop mechanisms, steppers function efficiently without feedback because the user can derive engine positions simply from counting incremental steps. In contrast, coupling a an encoder with a servo motor is essential to achieve inch-perfect movement precision expected from the engine type.
According to the classical definition, a servomechanism is an engine pieced together with a feedback sensor and a controller to form a closed-loop control circuit. In the circuit, the sensor orchestrates the following operations:
To obtain velocity or angular displacement data, an encoder in a servo motor can be replaced with a potentiometer, a resolver, or a Hall effect transducer. However, the alternatives demonstrate inferior robustness, responsiveness, and reliability in most cases.
Choosing a sensor to match a servomechanism requires exploring the specifics of the system where the assembly is supposed to be integrated, in particular:
An alternative is a hollow-shaft mounting arrangement, using a springed tether. The method eliminates the need for alignment and associated failures, but demands special measures to be taken to ensure electrical isolation from the drive unit. A third option is bearingless mount composed of a sensing element installed on the engine face and a magnetic element—on the shaft.
The choice is typically between incremental and absolute. Incremental mechanisms are intended mainly to track speed since they provide no exact indication of positions. Absolute transducers enable both speed and angular displacement monitoring, enabling the user to determine with certainty where the motor shifted as a result of executing a command.
The user should study carefully the environmental aspects: presence of chemicals, moisture, as well as particulates, and vibration. The characteristics serve as a basis to establish preferred motion detector specifications—the IP rating, explosion-proof design, etc. Say, IP50 sensors are suitable for environments with excessive dust generation, while IP52-rated ones are deemed to be waterproof.
Furthermore, the operating environment dictates a particular sensing technology. Optical transducers are resistant to electromagnetic interference, but susceptible to dust contamination. Mechanisms employing the magnetic technology are sensitive to factors, such as presence of an electromagnetic field or ferromagnetic particles.
Knowing application particulars is certainly both a necessity and a preclusion of making the wrong choice. In addition to the investigation of intended use, the user should match the specifications and conditions of a measured system to essential parameters of an encoder. The parameters include:
Finding a perfect match is rather about choosing an optimal combination of accuracy, resolution, and repeatability than getting maximum magnitudes. To illustrate, the best option to use in a robot would be a feedback component featuring average accuracy, but ultra-high repeatability.
The mechanisms are already matched with the drive unit and the controller, which saves the trouble of going through the selection process and designing the integration. All it takes to start getting feedback and driving your machinery with precision is to spend one and a half minutes to connect and launch your RDrive servo.
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