Upside down

20.10.2020 | written by Michael Pyper

Inverse pendulum – what is that?

They are familiar to us from the city images of many metropolises: Segways. From a physical point of view, single-axle scooters are nothing more than inverted pendulums that keep the tourist's head up by means of control and regulation. This is done with the help of electric motors and sophisticated sensor technology and software.

Wikipedia tells us: “The inverted pendulum is a pendulum that has its center of mass above its pivot point. At its highest point, it is in an unstable rest position. The inverse pendulum is one of the standard tasks of control engineering for the stabilization of an unstable controlled system.”

A piece of control engineering

Inverse pendulums place high demands on the control engineering. The goal is to swing an inverted pendulum up to the highest point and keep it there. This rest position is called unstable. Even the smallest interference is enough to set the pendulum in motion again. By measuring the angle in relation to the vertical, computer programs are able to calculate how to control a motor in order to make the pendulum swing back into its unstable rest position and to compensate for disturbances. This requires both efficient data processing and an adequate high-quality direct drive.

Find out what this has to do with drive axis

Drive axis have to move certain components in machines and systems to various locations with high precision in order to hold them in position against external loads. This often happens at speeds close to zero up to a maximum speed. It is a domain of very precisely controllable electromechanics. However, what if the mass is large and the space is small?

That’s where hydraulics comes into play, which combines exactly these capabilities. Every advantage has its disadvantage: Precision leaves much to be desired, especially at low speeds. In existing solutions, a lot of energy is wasted due to throttling losses in the valves.

There is another way

Bucher Hydraulics has set itself the objective of combining the best of both worlds, electric drive technology and hydraulics, in order to satisfy the increasingly stringent demands of politics and legislation to conserve as much energy as possible. The direct AX drive technology without valves brings hydraulics into new dimensions as a drive force. This technology combines the high force and power density of hydraulics with precision and energy efficiency of the electric drive technology.

“Hic Rhodus – hic salta” as the Romans said, “Prove what you can do, here and now!” Thus, Bucher Hydraulics drive and hydraulic experts quickly converted a test bench into an inverted pendulum. They put a lot of weight on it: 1.2 tons. This weight is not only made to oscillate by the AX-driven linear axis, but is also balanced in the vertical for hours in continuous operation without cooling, as the following video impressively shows: