Traditionally, automobiles, lawn mowers, airplanes, dishwashers and other products contain a wide variety of rigid parts connected by joints that are designed to be strong and stiff.
Compliant mechanisms are jointless, elastic structures that reduce costs and simplify product designs. These single-piece flexible structures elastically deform without joints to produce a desired functionality.
During the past two decades, engineers at Brigham Young University (BYU) have been at the forefront of compliant design technology. In 2002, Larry Howell, a professor of mechanical engineering, established the Compliant Mechanisms Research Group (CMR).
According to Howell, compliant mechanisms gain their motion from the deflection of flexible components rather than from traditional approaches using hinges and bearings. “Advantages of compliant mechanisms include compactness, low weight, reduced part count, low wear, ease of manufacture, reduced maintenance and high precision motion,” he points out.
Howell believes that compliant mechanisms offer unique opportunities for manufacturers. “[There are] opportunities to dramatically simplify topology of mechanical systems,” he claims. “[However there are] also some unique challenges, such as mass-producing [products] with long, flexible components connected to rigid sections.”
As engineers become more aware of compliant mechanisms and their unique benefits, there’s been increased interest in the technology. Recent applications that BYU engineers have been involved with include exercise equipment, electrical connectors, switches, sporting goods and mechanical components used in handheld electronics. In fact, since the CMR was founded, Howell and his colleagues have received more than 20 U.S. patents for innovations such as a continuously variable transmission and a compliant clutch.
“We have conducted a wide range of research projects,” says Howell. “They have been funded by government agencies and labs such as the National Science Foundation, the Air Force Office of Scientific Research, DARPA and Sandia National Laboratories, as well as by companies ranging from small startups to multinational corporations.
“[Our] projects have [ranged in size] from microelectromechanical systems to macro-scale devices,” adds Howell. “Projects have ranged from medical implants to consumer products to nuclear weapons.”
The CMR was recently involved in the development of an artificial spinal disc that duplicates the natural motion of the human spine. According to Howell, the device has the potential to alleviate severe pain and restore the natural motion of the spine—something current procedures can’t replicate.
Typically, the most common surgical treatment for chronic low back pain is spinal fusion surgery. Fusion replaces the degenerative disc with bone in order to fuse the adjacent segments to prevent motion-generated pain. “Unfortunately, patient satisfaction with fusion surgery is less than 50 percent,” notes Howell.
“To mimic the response of the spine is very difficult because of the constrained space and the sophistication of the spine and its parts,” claims Howell. “A compliant mechanism is more human-like and more natural. The one we’ve created behaves like a healthy disc.”
The team of BYU engineers built prototypes, machine tested the disc and then tested the device in cadaveric spines. The device they came up with is now being commercially developed by Crocker Spinal Technologies Inc. “It has a lot of promise for eventually making a difference in a lot of people’s lives,” claims Howell.
Last month, Howell and two of his colleagues published the Handbook of Compliant Mechanisms (John Wiley & Sons Inc.). “The first half of the book is dedicated to design, while the second half provides a picture glossary of compliant mechanisms and their various applications,” says Howell. “The book is intended to be used by working designers and engineers.”