Active Ball Joint Mechanism (ABENICS)
A new video was posted a couple of days ago showing an interesting movement setup where 4 motors operate a ball joint in an interesting way.
This novel movement method was published by Kazuki Abe, Kenjiro Tadakuma, and Riichiro Tadakuma. It was supported by the national project of the Program on Open Innovation Platform with Enterprises, Research Institute, and Academia from the Japan Science and Technology Agency. The full document can be found on the IEEE website.
This gear-based joint combines two orthogonal tooth structures to achieve combinations of two degrees of motion at any one time: orthogonal and linear, rotation and linear, and rotation and rotation.
This type of joint would be perfect for the robotic arms but the prototype has limited torque for that purpose but other than its novel design the use of this joint could end up a niche design as it is rather complex. It could prove to be useful as a general motion solution for joints but more specialized solutions offer far better power to torque ratio.
Regardless of its usefulness or complexity, it is still interesting.
The formation process of a cross spherical gear starts with the sphere.
The x–y plane teeth profile is then rotated around one of the axes then another leaving the gear teeth in the sphere. This method creates two poles at which meshing increases sliding contact so that the transmission efficiency decreases due to friction. So in practice, the surface of the tooth should be greased for the sleeve as a resin to reduce contact friction.
A normal spur gear transmission efficiency is expected to be similar to that of the spur gear, and the forward and backward efficiency should be symmetrical.
The setup can move 500g at a 30cm distance or 1.47 Nm and the backlash between the monopole gear and the cross spherical gear in the prototype was 0.13–0.34 deg. That torque is rather small when you look at it as it uses 4 brushless DC motors each 48.5W of power that is further geared. This should provide more power as just one of the motors, if we look at similar 12V at 4A motors, provide by itself around 1.4 Nm.
Manufacturing of monopole gear and the cross spherical gear can be done by 5 axis machining or 3D printing but that is not conducive to mass manufacturing but some ideas about lathe-like machining may also be possible using the cross spherical gear linear symmetry.
We will track the development and how if any implementation this movement solution is implemented.