Electric actuators—not just for heavy lifting anymore

  • 25-Sep-2009 04:44 EDT
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Robert D. Thikoll, Vice President and General Manager, Thomson Industries Inc.

Traditionally, the application of electric actuators in off-highway vehicles has involved the use of significant force to perform a task. A new trend in the industry finds lighter-duty applications where actuation is driven by electronic controls. This controllability makes it possible to add cutting-edge features that improve performance, ergonomics, safety, and cost. The result becomes a competitive advantage for the equipment manufacturer and a convenience for the end customer.

To illustrate the advantage of these applications, imagine that the driver of a construction excavator idles his engine in between jobs and then revs up the throttle later to power the hydraulic boom and shovel. Innovative construction equipment manufacturers are designing electric actuators such that the control system automatically increases the throttle as needed to operate hydraulic equipment and then decreases the throttle to return to the “idle” position when power is no longer required.

This approach saves fuel and reduces noise because the throttle operates only when the machine is doing work. Moreover, electric actuators reduce manufacturing costs and improve safety by replacing hydraulic lines with electrical wires.

Further advantage of electric actuation becomes evident when combined with microprocessor-based controls to achieve more complex motion. An example would be joystick inputs to a control that drives electric actuators and steers the tracks of a skid steer or commercial lawnmower.

Connecting the actuator to the vehicle’s control system makes it possible to improve safety and performance in this case as well, by setting limits on the speed with which the vehicle can be operated while it is turning or achieving complex motion through a simple input.

Along the lines of safety and performance, actuators have cropped up as a way to control spool valves. Today, spool valves are used widely in off-highway equipment to control the operation of hydraulic actuators. Normally the spool valves are located in the operator’s compartment while hydraulic lines run from the valves to the cylinders.

Putting these valves inside the cab raises significant safety and environmental issues because of the potential of hot, high-pressure hydraulic fluid leakage. Furthermore, this practice requires that the manufacturer extend long hydraulic lines, piling up cost, taking up space, and driving unnecessary design complexity. Use of electric actuators solves these issues by enabling the spool valve to be mounted out of convenience rather than necessity, and therefore it can be placed in safer locations within the unit.

Another field where electric actuators are taking root is in the critical adjustment of harvesting systems on agricultural equipment such as combines. The combine’s grain processing chamber takes the threshed grain and cleans it from its chaff by blasting it with air and running it through a sieve.

The airflow louver adjustment controls the volume of air flowing through the cleaning system and the louvers must frequently be adjusted to optimize the performance of the cleaning unit for various crop conditions. Too much airflow and you lose grain; too little airflow and the chaff isn’t blown out. Normally, the operator must climb down from the cab to make these adjustments, which reduces productivity. With electric actuators, this can now be controlled from inside the cab.

Finally, for systems that have feedback in them, the use of electric actuators in controlling remote functions is spreading rapidly—not just in the type of application where an actuator creates independent motion between two boat engines for added steering control, but also in applications where controls are integrated with the actuator and the device acts in a servo loop to meet unique positioning requirements. Adjustable limit switches and electronic load control may be introduced into play as the actuator follows an input signal from a PLC or an operator. In this manner, an actuator can open or close maintenance hoods on construction equipment, raise or lower a boom on a sprayer, or tie off a bale of hay on a baler.

As illustrated, electric linear actuators have moved beyond applications where they merely apply force to perform work and are making substantial progress in electronically controlled systems. Electric actuators save money and space by eliminating hydraulic lines and improve safety by performing what used to be manual tasks. OEMs and Tier 1 suppliers are increasingly turning to best-in-class motion control vendors to engineer a complete system rather than just components. OEMs can capitalize on these advantages by seeking out the vendor’s expertise early in the design cycle, which reduces total landed cost and ultimately delights the end customer.

Robert D. Thikoll, Vice President and General Manager, Thomson Industries Inc., wrote this article for SAE Off-Highway Engineering.

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