Hydraulic Linear Actuator Design Considerations

While there are many types of Linear Actuators ranging from the simple “roller screw” model to sophisticated electro-mechanical, pneumatic, piezoelectric, and hydraulic, a linear actuator generally refers to devices that convert rectilinear or electro-rotational motion into linear motion.  Hydraulic linear actuators refer to those classes of devices where an unbalanced fluid pressure applied to the piston can generate a large force that can move an external object.  While gas cylinders are useful in certain applications, the size and noise of gas compressors and their propensity for leakage at high pressure makes fluid mediums the implementation of choice for a robust, large force application.  Since hydraulic fluid oils are nearly incompressible, a hydraulic cylinder can provide controlled precise linear displacement of the piston for many kinds of applications.

Major Components of a Hydraulic Linear Actuator

A complete hydraulic linear actuator system consists of the following major components:

  1. A hydraulic pump, used to maintain hydraulic liquid pressure in the system
  2. A sealed piston cylinder assembly that allows a piston linear motion inside the cylinder.
  3. Hoses to pass pressurized fluid to/from the cylinder
  4. A system for measuring the precise position of the piston inside the cylinder.

A familiar example of a manually operated hydraulic actuator is a hydraulic car jack. Typically though, the term “hydraulic actuator” refers to a device controlled by a hydraulic pump and in our case, one capable of providing thousands of ft-lbs of force in service of heavy duty machinery and equipment.

Linear Position Measurement in a Hydraulic Linear Actuator

The kinds of linear actuators used in heavy duty machinery require accurate position sensing under some of the worst and most corrosive environmental conditions that exist.  Extremely high oil pressure coupled with high heat, corrosive salt and sand, sea water, EMI, and constant multi-frequency vibration mean that these hydraulic actuator assemblies must have extremely robust sealing and mechanical designs that reduce the number and complexity of moving parts while still providing reliable position sensing.

The CPI SL series of position sensors is based on a modern implementation of a draw wire sensor technology that has been around for decades, but with a twist.  Our unique LVDT based implementation converts the linear motion of the piston into the rotary motion of the spool which our LVDT then converts into linear displacement signals accurate to 1mm of position.  What’s more our system can provide absolute position measurement alleviating the need for startup offset calibration.  Gone are the complex electronics and vibration sensitive tubular waveguide used by failure prone magnetostrictive sensors.  CPI sensors are designed to be a high reliability drop in replacement for these sensors that requires no core drilling of the piston to insert.  Simply remove the magnetostrictive sensor waveguide and insert our sensor cable assembly into the hole left behind.  With a few turns of a wrench the sensor is installed.  Our sealed LVDT can then be installed on either the oil or the gas side, either internal or external to the cylinder.

See our SL series installation video to get an idea of just how easy it is to replace this.

Linear Actuator Design with CPI Sensors.

Control Products Inc. has been designing switches and sensors for specialized military and industrial markets for over 50 years. All our products are made and manufactured in the USA. If you are designing a hydraulic linear actuator for the kind of operating environment that requires extreme performance, then our sensors are a great fit in every sense of the word!

Please contact the CPI engineering team today to discuss your Linear Actuator design with our engineers.