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Contracting vs Expanding Actuators

Actuators are integral to our lives, from electric door locks in vehicles to prosthetic limbs for amputees. An actuator is a device that converts energy into motion. The form of energy can be anything from electrical to hydraulic. Traditional actuators tend to be rigid, but as technology has advanced, actuators have as well.

Actuators that can achieve muscle-like performance have been the future of robotics for a while. These actuators are more flexible, and they can be used in more settings than traditional actuators.

Muscle-like, or artificial muscle, actuators work in two ways—contracting (pulling) or expanding (pushing)

In our bodies, our muscles can only contract, or in other words, they can only pull. They cannot push, and because of this, muscles work in pairs. Think of it like your biceps and your triceps. When your bicep contracts, it bunches up and gets shorter, pulling the bone it is attached to. When it relaxes, your tricep is activated, and it pulls the bone back down. Contracting artificial muscles work this way as well. When power is applied to them, they contract and get shorter, pulling an object towards them.

Expanding actuators work in a slightly different way. While they are still soft actuators with muscle-like performance, they work by expanding when power is applied. This can simplify the system design for applications that need pushing motions. In some applications, instead of antagonistic pairs of contracting actuators, expanding actuators can be used.

Both actuators offer advancement to traditional actuators. Not only can they be soft, but they can also be quiet and highly efficient. Contracting and expanding actuators offer a muscle-like performance and can be integrated into any robotics project.

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