Time to rethink your servo actuator?

Actuators are no longer the reserve of automotive and welding applications. Today, they're used in a wide variety of industries. In these complex areas, it is important that the actuator can meet the specific needs of each industry, whether that's lifting heavy objects on a production line, delivering high accuracy in the electronics market or offering a lightweight package for a desktop robot.

For example, while welding, electronics assembly, packaging and palletizing applications demand relatively high accuracy, they pale in comparison to areas such as semiconductor manufacturing where nanometre accuracy is required.

One of the biggest challenges faced by modern servo actuators is the need to handle much heavier payloads. This is also true of Harmonic Drive's customers and over the last decade we've delivered a 90 per cent increase in the torque-to-weight capacity of our gearing component sets — improving from an average of 310Nm/kg to 580Nm/kg.

Positioning accuracy

Stepping into the realm of high-precision sectors such as aerospace and semiconductor manufacturing creates the need to use better positioning technology. A servo actuator may consist of a geared synchronous servo motor, combined with a positioning encoder, or controller, and an output bearing that supports the payload of the application.

This setup requires the encoder to calculate the angular position of the shaft, sending data through a feedback control system and allowing the system to achieve high accuracy. Depending on the application, the encoder used may take the form of an incremental encoder or an absolute encoder.

An incremental encoder works by generating a signal pulse when the shaft has turned a certain amount. The more signals it can generate per turn, the higher the resolution. However, a serious limitation of this kind of encoder is that when it is switched off, or if it suffers from a power loss, the encoder loses position and needs to home back to a reference point before it can start to count again.

While this characteristic is useful for automation environments where gates and levers only need to move through 90 or 180 degrees, it's less useful for actuators that need to travel through multiple turns of the shaft while handling silicon wafers. Here, any interruption in the power supply would cause the actuator to lose count and positioning accuracy.

In high precision applications, multi-turn absolute encoders are used instead. These work by scanning the position of a coded element on the shaft, translating it into an exact, or absolute, positional value. Absolute encoders are not affected by power loss, and can handle multiple turns of the shaft.

To tackle all these problems, Harmonic Drive has developed the FHA-C Mini Servo Actuator with multi-turn absolute encoder (MZE). The unit has been fitted with a specially developed precision output bearing with a high tilting capacity, allowing it to handle heavy payloads without additional brackets or support.

The absolute encoder in the device can precisely measure the motor shaft over the course of 600 revolutions. The system uses an EnDat 2.2 digital interface, which incorporates a power supply, transceiver and processor, all designed to comply with electromagnetic compatibility (EMC) regulations.

This gives it the added benefit of being able to operate in environments prone to electromagnetic interference (EMI) where the transmission of data can be subject to distortion if subjected to EMI.

As industrial environments become more diverse, they will demand more from components such as servo actuators. If engineers want to ensure that their applications can handle heavy payloads quickly and accurately, while maintaining a low profile, compact setup, then it may be time to rethink your servo actuator.