Robots manipulated by humans are being aggressively researched and developed. Such robots have requirements such as a large generative force, high-speed response, good controllability, high safety, low friction and backdriveability. The device is an all-purpose actuator that satisfies the demands for application in a human-coexistence welfare robot, such as power-assist systems. Additionally, the linear actuator shows possibilities of further improvement of the force-weight ratio by an increase of the ER gel structures. With regard to stabilizing the response of the linear actuator, spring elements contributed to its improvement. However, further stabilization remains as a future issue for practical use in human-coexistence robots.
An Actuator is one of the most important key elements of robots. Lightweight, compact, powerful, efficient and well-controllable actuators are essential for all kinds of robots. In addition, new actuators have a great potential for new robot applications. Examples are (1) micro actuators realizing inspection robots/invasive medical robots/micro flights/cell handling manipulators, (2) nano-positioning actuators realizing probe microscopes/atom-handling tools, (3) MEMS actuators realizing various kinds of robot sensors, (4) soft artificial muscles realizing human-support robots/bio-mimetic robots, (5) power actuators realizing rescue robots/construction robots and (6) actuators in ultimate environments realizing robots in nuclear plants/medical robots in MRI/space robots, etc.
Linear actuators are used in nearly every type of electrical device that requires a linear motion. Power drills, pumps, and other industrial appliances often rely on linear actuators to move other objects. Linear actuators are also used in some types of motors and are often used in the robotics industry to provide robots with motor skills. In fact, a simple piston inside of an electric motor or fuel-injection engine uses linear motion, and therefore acts as a Linear Actuator.
Linear actuators are expensive as hell yet pivotal in walking robot applications. This is only multiplied greatly when you consider the sheer number of actuators needed to make a robotic leg or arm come to life. Being someone that values the learning process more than buying off the shelf solutions (some may call it being thrifty or even confuse it for being stingy), I decided to do a bit of research on how a basic linear actuator works to try and see if I could cost effectively replicate one.
So how do most Linear Actuators work? Most linear actuators use a process known as the lead screw or ball screw process. In either case they function nearly the same. I will skip the full details of this process and focus on how it can be replicated.
First I salvaged a used 12V DC motor. It’s worth mentioning; the more torque the motor has, the greater force it will produce. Conversely, the slower it is. If you plan to purchase a motor, look at planetary gearbox motors, or motors with high torque.
Next, I wrestled with the idea of creating an aluminum housing to coordinate all the moving pieces. After nearly hours of bumbling through Home Depot, I ran across what was clearly the perfect fit; a piece of extensible PVC drain piping that had a pre-lubricated shaft. Ordinarily used for under the sink drain issues.
I went with a beefy 4″ long steel screw and a few steel nuts that match the screws thread count. The first screw was used as a stabilizer when I mounted the screw to the motor shaft. The next screw was embedded into the PVCs shaft and epoxied into place.
Finally, assembly. Under the minor constraints of the PVC housing, the actuator has ~2″ stroke. Either way, perfect for discovery and for the application I had in mind. At the end of the day, here is an itemized list of what was purchased/used. 12V DC motor – $5, PVC assembly – $3, steel screw with random hardware – $2.