Origami robots are composed of thin structures that can fold and unfold to change shape. They are compact and lightweight, but have functional restrictions related to size, shape, and how many folds can be created. On the other hand, modular robots use large numbers of individual entities to reconfigure the overall shape and address diverse tasks. These robots are more flexible when it comes to shape and configuration, but they are generally bulky and complex.
Taking inspiration from both origami robots and reconfigurable modular robots, researchers at EPFL’s Reconfigurable Robotics Lab developed a modular origami robot called Mori. It combines the advantages of the two types of robots into a versatile system that has the potential to overcome each type’s individual limitations.
The Mori module prototype is an equilateral triangle that is 6 mm thick, measures 80 mm long on each side, and weighs 26 g. Its low-profile triangular structure has a manual engagement mechanism and a folding actuation mechanism at each edge. Mori is mobile on flat surfaces, can be attached to other modules of its kind, and can fold into any 3D configuration.
Every slender module contains actuators, sensors, and an on-board controller. This means that the only external input required for full functionality is a power source. Each Mori module can be attached to another in any formation using a small, symmetrical coupling mechanism with a rotating pivot that provides actuation. Each side of a module contains both protruding and receiving elements of both mechanisms, allowing any side of one module to be connected to any side of another. Once connected, the modules can fold up into any shape.
Each self-contained module has three separate actuation systems. Actuation is provided by a stepper motor fixed in parallel to the engagement axis. A stepper motor was chosen because it has a fixed step size, permitting open-loop position control; provides a holding torque; and can be free to rotate if necessary. A planetary gearhead with a ratio of 256:1 is attached to increase the effective torque and reduce the step size.
A secondary gear system consisting of three spur gears is installed to translate the actuation from the motor to the engagement axis. A slotted pivot is attached to the final gear in the transmission system, forming the active part of the actuation mechanism. This U-shaped pivot forms the counterpart for an insert, which is integrated into the housing.
The actuation mechanisms of two modules are brought together when the passive part of one module is inserted into the pivot of another. When a torque is applied to the pivot, it causes the two modules to fold up on one another.
The engagement mechanism, which is operated manually, consists of a spring-loaded pin that enters the socket of another module. The pin is first retracted and the two engaging modules are brought together by aligning their engagement axes. The pin is then released so that the spring-loaded mechanism locks the two engagement axes to one another. A hinge is formed, restricting motion radially and axially so that only folding along the engagement axis is possible when any two modules are connected.
Mori’s electronics allow for various forms of closed-loop control to be implemented. Angular position sensors can be added to provide position feedback of the motors or the folding pivots. Other on-board sensors can provide position feedback based on the device’s kinematics, or external sensory systems can be implemented to provide the relevant control signals.