Actuators have always been on the frontline of automation, providing the “push and pull” that extends human capabilities to operate everything from delicate pick-and-place applications to 10-ton agricultural combines. Now, as the industrial world becomes increasingly digitized and connected, a new generation of actuators is fulfilling that role with more intelligence, simplicity, and economy, while overcoming increasingly challenging environmental conditions.
The Benefits of Integrated Electronics
By integrating electronics within the actuator housing, smart actuators enable switching, synchronization, and networking to be managed automatically based on signals from a common external source, such as a programmable logic controller (PLC) or other control unit (Figure 1). Participation in more complex automation schemes becomes feasible, and a more compact system footprint simplifies operation and lowers cost of ownership.
Key among the embedded functionalities that enable this integration are:
Low-level power switching. Traditional actuators often rely on large, power-inefficient relays or independent controllers to extend, retract, or stop the extension tube. By using onboard electronics to manage the power, current at the switches or contacts can be reduced from 20 A to less than 22 mA, which enables a simpler, less expensive system design. Actuators can be programmed to extend, retract, or stop the tube using low-current signals, providing a soft start. This improves safety by reducing the hazard of electrical shock, simplifies design by allowing lower-rated control components, and puts less stress on system batteries and charging systems.
Low-level power switching also improves position control by enabling dynamic braking control. Once the power is cut to an actuator, it could take between 5 and 10 mm to coast to a full stop, depending on how the actuator is mounted. Electronic actuators enable dynamic braking functionality, which can reduce that coast to about a half millimeter by electronically forcing a short between motor leads inside the actuator. This improves repeatability and positioning capability.
End-of-stroke indication. Knowing when the actuator has reached the end of a stroke is important for safety and performance reasons. If an actuator is used to lock a device into place, a simple LED light triggered by the output can confirm it is locked and will protect the operator from an unsafe condition. This functionality can also be configured to notify the end user of an end of a stroke, providing a safety interlock while also extending the working life of the actuator.
Bus operation. Integrated electronics make it possible for actuators to apply networking standards, such as the J1939 standard proliferated by the Society of Automotive Engineers to be the Controller Area Network (CAN) bus for heavy-duty vehicles. J1939 is a high-level communications protocol that provides a standard messaging structure for communications among network nodes under control of an electronic control unit (ECU). Every message on an actuator module representing a J1939 bus node has a standard identifier indicating message priority, data, and ECU source. This enables plug-and-play interchanges of supporting devices that share the same network and comply with the messaging structure.
A typical CAN bus network can be illustrated with four actuators using built-in CAN bus-compliant intelligence and connected directly to both a battery and control source (Figure 2). The green box represents gears, sensors, or other components that could also be connected to the network. The orange line represents the two-wire bus that transmits the low voltage of power needed for the system, and the blue line represents the wires that are used for information exchange.
Where J1939 is a communications protocol that is popular for off-highway applications, integrated electronics are increasingly applied in plant floor, material handling, and other applications. Actuators with integrated electronics can now be programmed to participate in networks and systems involving industrial communication protocols such as HART and network protocols such as Ethernet.
Such advanced position control and switching enable programming of the drive to perform with an infinite number of movement profiles and custom motion strategies. Users can, for example, program the actuator to seek forward a few millimeters or make a small set of movements back and forth to reach a 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.
Synchronization. With integrated electronics and networking, system developers will have much greater capability to synchronize operations among multiple actuators. Users of smart actuators will be able to configure start-and-stop instruction, and the actuator electronics will handle the synchronization.
Electromechanical actuators already provide advantages over fluid-driven actuators in heavy-duty precision applications by delivering absolute position feedback, but have traditionally done so with external potentiometers, encoders, limit switches, and controls. Integrating the components into the actuator provides additional benefits, enabling absolute analog or digital position feedback at every point in the stroke.
To provide analog position feedback, potentiometers simulated in the internal electronics send voltage signals that alert users of the absolute analog position, speed, and direction of the drive from beginning to end of stroke. They also remember that position, so if power is lost there is no need to return to a home position and reset the device. Because many mobile off-highway (MOH) machines are run by season and can sit idle for eight or nine months, it might sometimes be valuable to disconnect the battery to prevent it from draining. Without absolute position capability set at the factory, the user will have to recalibrate once they reconnect the battery.
Digital position readings can come from an integrated Hall Effect encoder, which provides a single-pulse-train digital signal to measure incremental position and speed. This improves control by indicating actual position changes and speeds.