Why Electric Actuators are Replacing Hydraulics

Hydraulics can provide the force required of many industrial applications. However, advancements in electric actuator technology over the last 30 years have made them a viable alternative.

Also referred to as electromechanical actuators, these devices are able to provide improved precision, flexibility and reliability with a bore size equivalent to that of hydraulic cylinders. Today’s electric actuators are also capable of exerting up to 100,000 lbs. of force, enabling them to compete with many hydraulic technologies.

This is not to say that hydraulics will be completely replaced by electric actuators in industrial applications. The high force, compact size and rugged design offered by hydraulic cylinders as well as the fact they are simple to deploy continue to make them a good choice for many types of industrial machines.

But there are also many benefits offered by electric actuators which have led to their increased use in recent years.

Three Reasons to Choose Electric Over Hydraulic Actuators

According to Tolomatic — a developer of electric, pneumatic and other motion components — there are a variety of reasons its customers are choosing to use electric actuators over hydraulic cylinders, but three main factors are driving the shift to electric:

•  reduced footprint and system complexity,
• fewer maintenance requirements, and
• motion control flexibility.

Design Simplicity 

The design of electric actuators is not as complex as that of hydraulics, which is one of the reasons customers choose them over the latter. As Tolomatic explained to Power & Motion, there are very few components in an electric actuator compared to a hydraulic system. Hydraulics require valves, regulators, hoses, hydraulic power units (HPU) and more. And there is the potential for any of these components to leak or fail over the life of a machine, the company said.

Reduced Maintenance

The lower maintenance requirements of electric actuators are helping drive their use over hydraulics as well. According to Tolomatic, electric actuation has very little to no maintenance over the life of a machine.

Use of planetary roller screws in electric actuators has enabled the longer life and low maintenance desired by many machine users, the company noted. In addition, the power elements (power screw and thrust bearings) of the actuator are usually greased for life. But in-field greasing methods can be used if needed.

The other component on an electric actuator which could wear is the rod seal. If failure occurs, though, the actuator can still operate as desired because it does not hold pressure like a hydraulic component would. And the seal can be replaced if damaged.

A hydraulic system typically requires routine maintenance to change the oil and filters in order to ensure continued performance. It may also be necessary to replace fittings, valves or other components over time.

Tolomatic noted there is also a growing lack of skilled maintenance people knowledgeable in hydraulics which is helping fuel the speed of adoption for electric actuation.

Hydraulic vs. Electric Actuators: Key Deciding Factors

Although there are many benefits to using electric actuators, there remain applications for which hydraulics are still a good fit.

Tolomatic said there is no doubt that hydraulic cylinders have the capability to provide great power density which means there are some machine installations where it is not currently feasible to utilize electric actuators. There are electric actuators available in the market capable of up to 50 tons of force, the company said, but forces above this point are less common for electric actuators due to the size of the screw/actuator and the availability and size of the servo motors. However, advances in technology may allow electromechanical actuation of higher force applications in the future. 

Understanding the working force required of an application is a key determining factor when choosing between electric and hydraulic actuators.

The company said it always works with customers to determine the true working force of a hydraulic cylinder. The actual working force needs to be calculated by looking at the pressure drop of the hydraulic fluid in combination with the diameter of the actuator cylinder. The costs of electric actuators and motors can vary more significantly than hydraulic cylinders and is often the key in getting a cost-effective electric actuator solution, said Tolomatic.

An advantage offered by electric actuators is the fact that force can be generated instantaneously unlike a hydraulic cylinder which has to wait for pressure to build up to create the required force. Adjustments to the actuator’s performance can also be done automatically because its servo controller regulates the electrical current used to power the device which is available as needed.

Conversely, the HPU used with a hydraulic system must always keep pressure in the system which can be difficult to do and thus can have an impact on response time and the ability to adapt to any necessary performance changes.

The environment in which a motion system will be used is also important to take into account. Temperature fluctuations, for instance, can impact the performance of hydraulic oil and thus the overall system. Additional components and maintenance may be required to keep the oil heated or cooled to an appropriate temperature so it can flow through the system as desired, ensuring consistent performance.

Electric actuators, on the other hand, are not typically affected by temperature. The actuators can overheat but that is often due to extreme changes in duty cycle, or it not being sized appropriately for the application.  And if used in a cold environment there are greases which can be used to ensure performance.

Noise is another environmental factor to take into consideration. Hydraulic systems tend to be noisy, which could be a concern for machine operators. Minimizing the amount of noise emitted from a machine through use of a quieter electric actuator can increase safety and comfort for operators.

This helps create a more desirable working experience, an increasingly important aspect as manufacturing – like many industries – is struggling to find skilled workers. Offering a safe and comfortable work environment not only aids employee retention but also the ability to attract new potential employees.

READ MORE: Understanding When to Use Hydraulics

Evaluating Total Cost of Ownership is Important

One of the biggest challenges associated with the switch from hydraulics to electric actuators is customers having knowledge and confidence in both technologies, said Tolomatic.

The company said there are many people who have been working with hydraulics for a long time but unaware or less comfortable with electric alternatives. Conversely, there are many people who are earlier in their careers and have grown up with electric technology which has provided them with a desire for more control and data collection, leading to a preference for electric actuators. They may also be less familiar with hydraulics which further influences their actuation technology choice.

More industry education on the pros and cons of each as well as working directly with a motion control technology supplier like Tolomatic can help provide a better understanding of both systems so a more informed decision can be made.

In addition, evaluating the total cost of ownership (TCO) associated with electric linear actuators versus hydraulic cylinders can help determine the best option for a given machine application. When doing so, Tolomatic points to the iceberg principle – the initial cost of a hydraulic cylinder-based motion system is less than that of an electric actuator one but there are more costs under the surface which can impact TCO.