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Industry and government are finding a wide array of uses for NASA Goddard Space Flight Center's compliant mechanisms. Originally developed for the mechanical isolation of sounding rocket assemblies and further developed during robotic research, these compliant mechanisms provide customized structural response and mitigate shock and vibration damage in applications as diverse as medical devices, industrial and recreation equipment, and ergonomic designs.

NASA seeks qualified users and/or manufacturers to pursue further development and commercialization of this innovative mechanical technology.

This technology was used by Connecticut-based Enduro Medical Technology to benefit PT patients, soldiers, and children.

NASA Goddard's compliant mechanisms are highly effective replacements for rigid connections between structures. They provide customized structural stiffness, facilitate coupling operations, and mitigate shock and vibration damage. Additional benefits include the following:

• Flexible: Compliant mechanisms provide structural stiffness and allow primary motion while permitting subtle twisting and cushioning.
  
  
• Controllable: The behavior of compliant mechanisms is well understood. Behavior is always better than predictions using standard techniques.
  
  
• Better shock absorption and vibration dampening: Compared to rubber isolators, NASA Goddard's compliant mechanisms provide instantaneous shock absorption, greatly reduced first resonance, and no higher frequency resonances.
  
  
• Robust: Cable is strong and lightweight. Stainless steel and coated cables can be used, providing corrosion and contamination resistance for application in hostile environments (e.g., at sea, in dusty conditions). NASA Goddard's compliant joints resist damage and are resilient across temperature extremes. Additionally, they deteriorate gradually, not suddenly, preventing problems caused by unexpected failure.
  
  
• Easily adapted to existing designs: An extensive array of cable sizes, lengths, and configurations can be used, allowing compliant mechanisms to be tailored to meet specific application requirements. The compliant mechanism design can be varied to provide increased flexibility or stiffness for a given volume constraint. In addition, they are compatible with other materials.

NASA Goddard's compliant mechanisms have a proven history in vibration dampening and robotic applications. However, the combination of structural stiffness and subtle twisting and cushioning allows these compliant mechanisms to replace rigid connections effectively in a number of other applications, including:

• Medical devices: NASA Goddard's compliant mechanisms offer a low-cost alternative for joints in prosthetic and physical therapy devices. In addition, these compliant mechanisms duplicate the rotational movement and flexibility of a natural joint by providing resistance that is similar to human limbs; as the cable bends, the stiffness increases. Good shock absorption also helps to provide a more natural feel.
  
  Compliant mechanisms with differing DOF can be developed to simulate several physical joints including the knee, hip, and ankle.
  
  
• Couplings/joints/hinges: Applications for compliant joints include the following:
  • Door hinges
  • Roller coaster connectors
    
  • Trailer hitches
  • Trains
  • Universal joints
  • Cargo holds
  • Guard rails
  • Mower decks
    
    
• Robotics: Robots perform an array of tasks in numerous industry applications. Regardless of the application or environment, end-of-arm tooling is the critical robotic component that allows machines to grasp, weld, paint, grind, or perform any number of other functions.
  
  NASA Goddard's compliant mechanisms can provide robotic arms and end-of-arm tooling with sufficient flexibility to move in any direction and rotate about any axis while compressing and absorbing any misalignment. This enables robots to mimic human capabilities used in manipulating objects and can help prevent damage to precision components during assembly operations.
  
  
• Bumper systems: Manufacturers and insurers alike recognize that energy absorption is a key design criterion for vehicle bumper systems. The shock absorption properties provided by NASA Goddard's compliant mechanisms facilitate safe and cost-effective bumper system designs.
  
  Bumpers typically consist of a plastic cover with a reinforcement beam made of steel, aluminum, or plastic. An energy absorber often is included between the outside cover and the reinforcement beam. With shock absorption properties that are not temperature dependent, these compliant mechanisms are an effective, low-cost replacement for the polypropylene foams and plastic honeycombs frequently used for energy absorption.
  
  
• Commercial and industrial equipment: NASA Goddard's compliant mechanisms are capable of providing simultaneous shock and vibration attenuation across temperature extremes for individual components or entire systems. An extensive array of cable sizes, lengths, and configurations are available that allow compliant mechanisms to be tailored to meet specific application requirements. These compliant mechanisms are well suited to various applications:
  • Mobile electronics
  • Avionics equipment
  • Appliances
  • Laboratory equipment
  • Pumps and motors
  • Generator sets
  • Shipping containers
  • Computer equipment
    
    
• Ergonomic design: Mismatches between the physical requirements of the job and the physical capacity of the worker can lead to work-related musculoskeletal disorders (WMSDs). Repetitive motions, awkward working positions, and vibration are risk factors that increase the probability that employees will develop WMSDs. In 1996, U.S. workers experienced more than 647,000 lost workdays due to WMSDs. These injuries cost businesses $15 billion to $20 billion in workers' compensation costs each year with indirect costs running as high as $45 billion to $60 billion.
  
  NASA Goddard's compliant mechanisms offer a means to limit vibration exposure to the human body and reduce the likelihood of developing WMSDs. Suggested applications include the following:
  • Joysticks
  • Reciprocating power tools
  • Jack-hammers
  • Rivet guns
  • Hammer drills
  • Seat suspension
  • Autos
  • On/Off highway trucks
  • Construction and earth moving equipment
  • Office and factory seating
  • Material-handling equipment
  • Standing operators
  • Seated operators
    
    
• Sporting goods and recreational equipment: Many sports and recreational activities require motion control and shock absorption. NASA Goddard's compliant mechanisms offer an inexpensive means to combine flexibility, shock absorption, and variable resistance through a range of motion.
  
  Potential sporting goods and recreational equipment applications include the following:
  
  
  • Training shoes: Compliant devices acting as motion-limiting dampers can be incorporated into training shoes, such as those used by basketball players, to increase resistance.
    
    
  • Skates: Skateboards and scooters use trucks for suspension and turning. Compliant mechanisms offer a means to improve shock absorption while providing the selective directional control and flexibility required for turning.
    
    
  • Bindings: Ski and snowboard bindings require stiffness for support but need flexibility to ensure proper release and movement. Compliant mechanisms provide these important features.
    
    
  • Suspension systems: All-terrain ride-on toys, bikes, and playground equipment typically provide little or no suspension. Complaint mechanisms offer a low-cost means to provide suspension systems in these applications.

NASA Goddard Space Flight Center has developed a compliant mechanism technology that facilitates coupling operations, provides customized structural response, and mitigates shock and vibration damage. In structural connections, these mechanisms provide compliance and dampening. They permit motion in the primary direction and selective motion in other directions. This provides subtle cushioning, twisting, and realignment, which allows mating and contact surfaces to conform to each other.

The essential functional element-the bending element-of NASA Goddard's compliant mechanism consists of a short cable section. The configuration and material are varied according to the specific application requirements. The bending element is constrained at each end in cantilever fashion (see Figure 1).

Motion

The key to all compliant mechanism properties is the behavior of a single cable element. A single cable element operates in five independent directions, or degrees of freedom (DOF), out of a possible six. Referring to the axis designations in Figure 2, one end moves laterally in x and y with respect to the other but is constrained in z. The cable element is free to rotate about all axes. The cantilever attachment (which keeps the cable normal to the interface) contributes to the mechanism's stiffness and limited motion. Many of NASA Goddard's compliant mechanisms use basic cable properties to restrict DOF. (Mechanical stops also can be incorporated into the mechanism design.)

Performance

Cable compliance is used for two purposes: energy absorption and adaptable motion control.

Energy absorption, or dampening, is measured through static and dynamic loading. The sample response curves given in Figures 3 and 4 demonstrate the energy-absorbing capabilities of stranded cable. Figure 3 shows the benefits of low-resonance amplitude and the absence of higher order modes.

Figure 4 shows the nonlinear response and energy-absorbing qualities of the cable material. The hysteresis loop indicates energy input to the cable element.

Compliance, or adaptable motion control, is measured in the secondary, out-of-plane motions caused by the primary motion or external forces. The simplest examples are in Figures 2a and 2c. Translation along the x axis causes a slight contraction in the z direction; lateral motion accompanies rotation about the x and y axes. As these simple elements are built up into complex configurations, customizable compliant behavior is attainable.

Figure 5 shows cable elements arranged in a single-file row. This arrangement prevents rotation about 1 lateral DOF and reduces rotation about z, or the vertical DOF.

Figure 6 shows an array of cable rows arranged in a grid pattern. This arrangement prevents virtually all rotations and results in a 2 translational DOF device (top plate is shown as transparent).

The biggest benefit of compliance is the ability to divert unwanted primary motions into secondary directions. This allows coupling and mating operations to proceed smoothly and resonances to be "de-tuned." The basic building blocks described above can be arranged in custom configurations to provide varying DOF and compliance.

Controlling the Amount of Compliance

The amount of compliance in NASA Goddard's mechanisms can be controlled by adjusting the following cable characteristics:

• Cable size: Increasing or decreasing the cable diameter provides the most effective means of changing stiffness. Generally, orders of magnitude changes are possible by increasing the cable diameter by 50%.
  
  
• Cable length: Using shorter cables provides greater stiffness, while more flexibility can be achieved with longer cables. There is a practical limit to the segment length based on material choice and strand size.
  
  
• Preloading: Stiffness can be increased by up to 10 times by incorporating preloaded cable segments where the cable is already bent in the unloaded configuration.
  
  
• Cable type and material: The cable type (e.g., twist, stranding scheme) can be varied for finer control of the stiffness. A cable with fewer but thicker strands is stiffer and provides less dampening than one with more, finer strands.

Patents

The following patents are included in NASA's compliant mechanism patent portfolio (patent links open new browser windows):

* 4,932,806: Compliant joint
* 4,946,421: Robot cable-compliant devices
* 5,174,590: Compliant walker
* 5,257,669: Climbing robot

For information and forms related to the technology licensing and partnering process, please visit the Licensing and Partnering page. (Link opens new browser window.)

If you are interested in more information or want to pursue transfer of this technology, please contact:

Innovative Partnerships Program Office
NASA Goddard Space Flight Center
Greenbelt, MD 20771
Phone: (301) 286-5810
E-mail: techtransfer@gsfc.nasa.gov