Updated: May 7, 2022
Pneumatic bladders are soft pouches filled with air. The pouch may stretch, like a balloon, or may be flexible, like a polymer, but it is always a soft, compliant material. Pneumatic bladders, a type of pneumatic linear actuator, are commonly used in applications that contact delicate objects due to their ability to conform to the shape of the object. Pneumatic bladders are also used in applications that contact the human body because they can be designed to optimize for comfort. Some examples include:
AR/VR haptic accessories
Bedsore prevention devices
Massage chairs and products
Treatment devices for lymphedema, deep vein thrombosis, limb ulcers, cystic fibrosis
Recovery devices for athletes
G suits for pilots and astronauts
Blood pressure monitor cuffs
The individual pneumatic bladder would be a quiet and inexpensive solution if it could stand alone, but it requires a supporting system of an air compressor or pump, hoses, valves, and connectors. The resulting system is large, heavy, noisy, inefficient, and expensive. Air-based systems, including pneumatic bladders, pneumatic linear actuators, pneumatic rotary actuators, and pneumatic cylinder actuators, also have slow response times and low bandwidth due to the limitations of air as a working medium.
Size and Weight
Pneumatic bladder systems are heavy and bulky due to the number and size of supporting components. It’s not just the size and weight of the pneumatic bladder that must be accounted for, but also the supporting components. The compressor/pump and driving motor are typically the largest and heaviest components of a pneumatic bladder system, but the valves, connectors, and hoses can also be significant contributors to the overall weight and size of the system.
Significant noise is emitted from the compressor/pump, the driving motor, and the valves. This often requires a muffler in the system and noise dampening design around the system, such as dense foam, which can have unintended consequences like additions to the size and weight or low heat transfer properties resulting in the system overheating.
Compressed air systems in industrial settings can have efficiencies as low as 10-15%. Compressing air takes a large amount of energy because significant heat is generated and is an efficiency loss. With pneumatic bladder systems, the compressor/pump not only has electrical and mechanical losses, but also the inevitable leaks in the hoses and valves reduce the efficiency of the whole system.
The compressor/pump and driving motor are expensive components of a pneumatic bladder system. Depending on the number of pneumatic bladders in the system and the complexity of their behavior, the valve block, connectors, and hoses can also add up to a large cost. This only accounts for the hardware cost of the system, the electrical power cost to support an inefficient system and an aggressive scheduled maintenance program can make the total ownership cost of a pneumatic bladder system very high.
Speed and Bandwidth
The response speed of pneumatic bladder systems is limited by the response speed of compressed air. It can be fast with very high-pressure systems, but high-pressure pneumatic bladders are very rare. Most pneumatic bladder systems are low pressure and operate very slowly. Air response time is also a serious limitation to the achievable bandwidth of the pneumatic bladders.
One popular alternative to pneumatic bladders and pneumatic linear actuators are soft electric actuators, such as the HASEL technology offered by Artimus Robotics. Visually, these appear similar to pneumatic bladders because they consist of a filled polymer pouch, but the pouch is filled with a commodity oil instead of air, maintaining a soft, compliant structure. As an entirely electric system, HASEL actuators offer extremely fast response times, very high bandwidth, and variable actuation profiles, allowing for expanded features and sensations in products that were previously limited by the pneumatic bladder to slow speeds and simple actuation profiles. For example, HASEL actuators can be synchronized with music to provide end-users with new experiences. As an alternative to pneumatic bladders, HASEL actuators don’t require a supporting system of components, just small electrical wires. These actuators are lightweight (no metal parts) and compact (thin form factor), and they operate silently. Due to the simple bill of materials of commodity components, HASEL actuators are extremely inexpensive at a mass-production scale. They also have the efficiency benefit of an electrical system (minimal waste heat generation), and most interestingly, HASEL actuators have intelligent self-sensing capabilities, allowing for real-time feedback and closed-loop control.
An overview of HASEL actuators and example applications can be found in the video below. If you are interested in learning more about why HASEL soft electric actuators from Artimus Robotics are rapidly replacing pneumatic bladders, please contact email@example.com.
About Artimus Robotics
Artimus Robotics designs and manufactures soft electric actuators. The technology was inspired by nature (muscles) and spun out of the University of Colorado. HASEL (Hydraulically Amplified Self-healing ELectrostatic) actuator technology operates when electrostatic forces are applied to a flexible polymer pouch and dielectric liquid to drive shape change in a soft structure. These principles can be applied to achieve a contracting motion, expanding motion, or other complex deformations. For more information, please visit Artimus Robotics or contact firstname.lastname@example.org.