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FEATURE MOTION CONTROL


consumption and battery drain. Dynamic braking control is another


benefit of low-level power switching. Once the power is cut to an actuator, it could take 5-10mm to coast to a full stop, depending on how the actuator is mounted. Electric actuators enable dynamic braking functionality, which can reduce that coast to about 0.5mm by electrically forcing a short between motor leads inside the actuator. This improves repeatability and positioning capability.


Programming caPability Such advanced position control and switching enable programming of the drive to perform with an infinite number of movement profiles and custom motion strategies. For example, users can program the actuator to seek forward a few millimeters or make a small set of movements back and forth to hunt down the desired position. And because the system knows what it is supposed to do and monitors performance in real time, it can flag potential variances and trigger advanced algorithms to manage further alarms, corrections, or shutdown. With CAN bus, system developers have much greater flexibility to


program the sensors and internal electronics to synchronise operations among multiple actuators. For example, they can program units to vary in speed depending on load or change speed to compensate if units speed up or slow down. Electric actuators without CAN bus can provide absolute position readings,


but they typically require significant power, heavier wiring, relays and other space-consuming and vulnerability prone wiring. CAN bus enables all of


Figure 2. Thomson smart electric linear actuators feature simplified control architectures embedded directly into their electronics. This enhancement allows for a number of functional and control benefits


this to be embedded directly into the actuator and managed by embedded, low-level switching connected to the 2-wire CAN bus communications network and two power wires. This not only simplifies wiring in the machine but also brings all of those previous external electronics into the product – and warranty – of the actuator vendor.


Diagnostics anD maintenance In addition to returning real-time position data to the user, CAN bus-enabled actuators are constantly returning results of ongoing monitoring of


temperature, current, speed, voltage and other variables, which enables advanced diagnostics and error handling. Feedback can arrive as quickly as ten times per second as the actuator constantly tests itself. If it detects a problem, such as surpassing a temperature threshold, the actuator finishes its programmed move – either fully retracted or extended – stops and sends an error flag to the computer, all in fraction of a second. Here are some of the variables that can now be monitored with unprecedented efficiency: Current: Current monitoring is a critical safety feature that shuts down


the actuator on overload and eliminates the need for the traditional noisy mechanical clutch. Voltage: Continuous monitoring of voltage protects the actuator by


preventing motion if it detects it operating in an environment outside of the acceptable range. Temperature: Internal temperature is monitored and, if it is outside the


acceptable range, the actuator is shut down after extending or retracting stroke. Built-in temperature compensation allows the actuator to push the rated load at lower temperatures without nuisance tripping. Load: Trip points can be calibrated at assembly to assure repeatable


overload trip points independent of component and assembly variations. This not only assures repeatable performance but also relieves the user of having to recalibrate in the field. All such functionality can now be embedded within the actuator, available


instantly and, via the network, potentially sharable for assistance with external troubleshooting. Thomson smart electric actuators, for example, are a plug-and- play solution, easily swapped out in case of a problem (Figure 2, above). On the other hand, replacing a problematic hydraulic cylinder could involve a service call from the manufacturer and hours or even days of disassembly, reassembly, system bleeding and testing – time that would be better spent in production. Moreover, system health monitoring can occur remotely. For example, an


OEM support technician in Iowa can log in to a combine in North Dakota to diagnose a failed actuator by analysing electronic message flags on temperature, position, current and input voltage.


enriching the Dialogue In many ways, optimising the performance of an actuator is a function of the dialogue quality between the users and the device. With a CAN bus- compatible language combined with advanced embedded electronics, users have more flexibility in telling their actuator where and how fast they want it to move, and when they want it to stop; and they will get instant feedback as to whether it has behaved accordingly. You can engage in this kind of dialogue with a non-CAN bus electric


actuator, but it requires more external switches and wiring. You can also engage with a hydraulic cylinder, but it is a far longer and much more complicated conversation. By utilising a common, highly efficient language, the CAN bus standard moves the discussion from how the communications will be managed to what exactly the user wants to accomplish. Whether you are using J1939 programming in automotive MOH industries


or CANopen in industrial automation, the result can be greater control and design flexibility, faster engineering, more efficient installation, and overall lower cost of ownership.


Thomson www.thomsonlinear.com


4 DESIGN SOLUTIONS MAY 2022 4


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