How to Convert Hydraulic Actuators to Electric

Total Cost of Ownership

Besides improvements in motion control, there are other factors that contribute to the overall total cost of ownership.  In many cases, if all these factors are considered over a reasonable life of the equipment, the electric actuator system will have a lower total cost of ownership.  These factors include:

• System components – Hydraulic systems require more components to purchase and maintain.

• Footprint – Although hydraulic cylinders are compact, the overall footprint of an electric actuator system is typically much smaller when factoring in the footprint of the hydraulic power unit, allowing for a more compact and efficient machine design.

• Life – The life of electric actuators can be estimated with a L10 calculation & dynamic load rating while the life of hydraulic cylinders is extremely hard to predict. Download "Calculating Total Cost of Ownership" Infographic. Electric actuators allow users to better calculate and select an actuator that meets their system life requirements.

• Efficiency – Electric actuator system efficiency is typically in the 75-80% range while hydraulic systems typically realize around 40-55% efficiency.

• Utility costs – Due to efficiency, hydraulic actuators can consume 2-3 times the amount of electric utility each and every year. Download "Electric vs. Servo-hydraulic vs. Hydraulic Actuators" Infographic. 

• Maintenance -  Electric actuators require very little maintenance, hydraulic systems rely on seal integrity through the system for proper performance.  Due to wear, temperature, and other factors, seal integrity will diminish and performance along with it.

• Temperature – With high / low temperature grease, electric actuator can operate in temperature extremes minimal effect on performance.

• Leaks and environmental concerns – Only a matter of time before hydraulic systems will leak.  Leaks can be safety hazards as well as contribute to many environmental concerns.

• Data collection – Servo systems used with electric actuators provide position, velocity, and force/torque data at all times to the control system and better monitor processes.

• Other factors – Noise, shock loads, side loads

Determining the work being done by the hydraulic cylinder to appropriately size the electric actuator

Once the decision has been made to convert from hydraulic cylinder systems to electric actuators, the biggest and most costly mistake that machine designers make is to make an oversimplified force calculation of pressure (remove extra space)  multiplied by the area of bore size.

Force = Area x Pressure

Since hydraulics are high pressure systems (typically 2000+ psi or 140+ bar), theoretically they can achieve very high forces, but in practice are typically not deployed near their peak force capabilities.  Additionally, the jobs that hydraulic cylinders perform usually do not require full force over the full stroke. In most cases, the force profile will change over the length of the stroke.  For example, a pressing application may only have high forces for a very small portion of the stroke and be virtually unloaded during the approach and retract portions.  Because of these reasons, it is important to take a little time to make some pressure measurements at the cylinder or valve in order to better determine true applications forces.  It is quite a simple procedure and Tolomatic has created an easy to follow guide on how to make pressure measurements in a hydraulic cylinder system.

Along with force, electric actuators must also know the speed and duty cycle of the application in order to properly size the application.  Watch the video (above) on how to convert hydraulic cylinders to an electric actuator alternative.  Again, it is a simple process to determine with readily available tools such as a phone and a ruler.  Take a video of the motion cycle with time stamps and measure the distances.  Combine this with the pressure measurements to estimate force, and you have everything you need to size an electric actuator alternative.

Creating an electric actuator system

Once the proper measurements have been taken and the actuator can be sized.  To make it easy, Tolomatic has an online sizing software tool to input the motion and force details to select the proper electric actuator for the job.  Decisions will need to be made on gearing (ratio), motor size (torque vs. speed), type of power screw (ball or roller screw) and also considering the environment (temperature, contaminants, etc..) that the actuator will be deployed in.