Cary, NC —Seeking a simple, low-cost alternative to traditional servopneumatics, engineers are becoming interested in the decades-old MR fluid technology. Digital-signal processing and faster computing speeds are providing MR fluid with performance characteristics that rival electromechanical technologies, but at a fraction of the cost.
MR fluid changes from a fluid state to a semi-solid state that is directly proportional to the magnetic field applied to it. The material contains magnetic particles that form a dense network of chains when a magnetic force is applied to them. When the magnetic force is removed, particles revert to their free, unchained form and allow movement of pneumatic actuators.
Several manufacturers of pneumatic and rotary-actuated products—including Parker Hannifin Corp., PHD Inc., and Turn-Act Inc.—are drawn to MR fluid technology for its ability to provide servo-like control. The new generation of MR-enabled motion control products provides precise stepping functions, infinite positioning capability, and simplified operation compared to electromechanical technology.
"MR technology provides the type of control for pneumatic actuators that was previously reserved for electric servo products," says Brian Pate, a mechanical engineer at Turn-Act Inc. (Jeffersontown, KY), a maker of rotary actuators. Pate believes that MR technology will erode some of the base of business that is currently served by the electric servo and stepper products. He also notes that MR technology could replace applications currently addressed by shock absorbers and other pneumatic servo valve systems.
"We believe there is opportunity to apply MR technology to all pneumatic actuators," says Pate. "It allows near programmable robotics at a very affordable price," he says.
PHD (Fort Wayne, IN), a manufacturer of rotary products, uses an MR brake in its RA rotary actuator. "We expect the actuators to provide all the benefits of a pneumatic device normally controlled with stepper/servo motors or proportional valve systems," says PHD's Glen Morr, a mechanical engineer. "Where I see this technology mainly being used is as a replacement for the hard-stopped multi-position rotary actuators."
Morr points out that MR technology has numerous advantages that make it desirable. "The MR rotary actuator is less costly than hard-stopped multi-position actuators, the positions are programmable, and it requires one standard pneumatic valve as compared to a hard-stopped multi-position rotaries that require a valve for every position."
Morr believes the MR approach to motion control will fill the performance gap between costly all-electric motion control and simple, pneumatic hard-stopped positioning. "It provides the power and simplicity of pneumatics with control that approaches that of servos," he says.
"A rheonetic actuator is just as repeatable as servo control, given the same parameters," says Doug LeRoy, an engineer who develops and manages pneumatic applications at Lord Corp. The system cost is 55-70% of a comparable electromechanical system, he says.
LeRoy says that weight of metallic MR fluid may be a concern in some applications. "Weight was a consideration in one project involving a prosthetic leg, but we engineered around that," he says.