The ABENICS Active Ball Joint Mechanism Moves an Output Link with Three Degrees of Freedom
See how one team designed and built a mechanism that can rotate an arm with up to three degrees of freedom in a compact space.
Traditional robotic joints
When imagining a robotic arm, you'll probably think of a mechanism that contains several axes of motion that are each driven by a single motor and gearbox. This works fine for most applications, but in circumstances with spacial constraints, the added bulk can get in the way. Also, including another degree of freedom requires extending the arm even further and adding more motors.
What can a spherical joint do?
Now imagine a mechanism that works more like a shoulder join that an elbow, where the output link can rotate in several axes in a much smaller space. Although the strength of this style of joint can be less than a traditional single-axis one, the freedom afforded by this novel design more than makes up for it. Robots can use the ABENICS Active Ball Joint Mechanism in situations requiring complex and precise movements in small areas, such as food service or manufacturing.
The central gear
Almost all of the "magic" is contained within the specially-designed spherical gear. Even though it looks really complicated, the gear can be best described as a pair of 2D gears that have been revolved around the X and Y axes, thus giving the appearance of a golf ball. This allows the central gear to be pitched, rolled, and slid along both drive gear axes. The output link is attached to a single pole on the end of the gear.
Designing the two drive modules
What good is a ball joint without any way to move it? The drive gears are shaped like the central gear, except they are revolved around just a single and can rotate in two axes: pitch and roll. To accomplish this, the project's team placed a bearing through the gear and added a differential pinion to pitch the end up and down. Behind that is a linkage that rotates the entire end when the rear helical gear is spun.
A pair of motors are mounted just above the two helical gears in a perpendicular fashion to save space.
Assembling and running the device
With everything designed, the team went ahead and printed/machined all of the required parts, including the central spherical gear and a pair of drive modules. Based on the positions of the two drive gears (perpendicular or opposing), the resulting motion can differ substantially.
To read how the team design, built, and drove this mechanism, you can view their paper in the IEEE journal here that delves deep into the math behind it.