SMD4 Encoder Module Now Available

Posted on Thursday 30th January 2025 at 12:00

The SMD4 is now available with its optional encoder module. This can be selected on the SMD4 with option code “E”. This blog will discuss the features of the SMD4 encoder module, as well as the upgraded AML device control software that is accessible with the SMD4.

The SMD4-E is compatible with incremental and absolute encoders. This means that AML can now provide a complete configuration from a UHV mechanism with an encoder to the stepper motor and encoder driver. This includes all in-vacuum connectors, feedthroughs, and airside cabling.

New Features:

With the release of the SMD4-E, we are also releasing a powerful new version of the AML device control software and updated firmware for the SMD4. This includes brand new features relating to the configuration and control of encoders, alongside significant updates to how users can configure AML stepper motors. New features include:

Encoder module.
Closed loop control.
Configuring units.
Configuring presets.
Virtual limits.

Encoder Module

The SMD4-E encoder module allows the real mechanism position to be read, independent of position as determined by the step count. Encoders make closed loop control, in which the actual position and target position are continuously monitored and the corrections automatically made to minimise error, possible.

Supported types	Digital incremental and BiSS absolute
Power	5V at 250 mA max. is available to power the encoder, protected by self-resetting fuse.
Connection	Female 26 way high density D-Sub. Encoder connects via adapter cable according to encoder type. Adapter cables for supported encoders are available from AML.
Incremental encoder support	Digital (RS422) incremental encoders having differential A, B and Z signals.  Single ended P and Q limits signals are supported. Maximum clock rate 1 MHz.
Absolute incremental support	26 bit BiSS-C (support for other bit depths may be added via firmware update)

The encoder module closed loop control functionality is discussed below.

Closed Loop Control:

The key benefit for users with an AML mechanism featuring an encoder and an SMD4-E will be the utilisation of closed loop control. Without an encoder, the SMD4 functions as an open loop system. It uses an internal step counter to track position of the motor, but there is no feedback to the SMD4 that the motor has performed a movement as instructed. Provided the motor maintains synchronicity this can be an accurate method of controlling stepper motors. However, many applications require greater accuracy and the certainty that the motor is in the desired position. This is where the SMD4-E’s closed loop control feature will be essential for many users. In closed loop control, the SMD4-E monitors the actual position of the motor via the encoder and automatically makes corrections to ensure the motor travels to and remains at its target position within a specified tolerance band. This can correct for many sources of error, for example, lost steps, backlash, inaccuracies in the mechanism and deviations of the mechanism due to applied load or temperature effects.

More details on how closed loop control works on the SMD4 can be found in the SMD4 user manual by clicking here.

In the above video, the encoder's endpoint correction is demonstrated. The encoder is maintaining the stage's target position despite external forces manipulating the table.

Configuring Units:

With previous AML stepper motor drives, users have only been able to use “steps” as the unit for all movements. Steps remain the core and default unit of the SMD4, but with the latest version of the AML device control software and SMD4 firmware, users will be able to configure the units of movements to their preference. For example, microns or millimetres for linear stages and degrees for rotation stages. This new feature provides a more natural way to work with mechanisms without having to think about conversion ratios between steps and the move you want to make. Additionally, there is the option to keep speeds and accelerations in steps, while using the specified unit for distance, as this often makes more sense when configuring dynamic properties of the motor.

Configuring Presets:

Configuring the drive for a new mechanism can involve entering a significant number of parameters. The latest SMD4 firmware comes loaded with default configurations for most AML mechanisms. Simply choose the required preset from a list in AML Device Control software, and a suitable default setup is applied. Users can start making movements right away in their chosen unit. Users can continue to refine the settings as required for their application and save the resulting configuration.

Full details on presets can be read in the SMD4 manual by clicking here.

Virtual Limits:

The SMD4’s range of motion limiter and virtual limits are a new feature designed to improve control of your stepper motor and mechanism. Virtual limits are specified on the AML device control software as a range. If the motor is given a command which drives it outside of this limit while it is active, the command is converted to a move to the virtual limit position instead, so that the motor is not driven outside of this range. If an encoder is active on the stage and the stage is forced outside of the range of the virtual limit (for example, the mechanism is forced by hand), then this is reported to the user through the device control software.

Limits can be set in your preferred unit. For example, when using a rotation stage you can set a limit of ±90° of your zeroed position. This removes the need for converting steps to your unit of choice.

Virtual limits can be determined without an encoder present but note as the position is open loop and the real position of the stage is not monitored, if the stage is forced outside of the range, then this is not reported to the user.

The SMD4-E is now available for sale and the latest version of the AML device control can be accessed through the latest update. If you have any questions about the SMD4-E, please contact us at sales@arunmicro.com.