The Future of Robotics Is in Good Hands

A typical robot consists of many parts, such as legs or wheels to get around, computer vision and other sensing systems, processing units for motion planning, and arms and hands to manipulate nearby objects. All of these components need to work in perfect concert to carry out any kind of meaningful task. But as the old proverb goes, a chain is only as strong as its weakest link — and the same goes for robots. If even one of these systems is lacking, the robot’s capabilities will be severely limited.

Artificial fingers are a weak point for nearly all robots in existence today, especially those that are designed to replicate activities normally carried out by humans. To handle the fine, dexterous, and sometimes forceful manipulations required of such activities, a robotic hand must be very much like a human hand. And that means it must be capable of fast movements and a strong grip. It must also be able to comply with objects to get a secure hold of them. Moreover, it is essential that the robot hand be close in size to a human hand so that it is able to work with standard tools.

These requirements are exceedingly difficult to meet, however. To supply enough torque, the actuators must be quite large, which makes the hand bulky and unable to move like a human’s. Previous efforts have worked around this issue by locating the actuators in the forearm and routing artificial tendons into the hand. But this is a very complex and expensive solution, and it has also proven to be fragile.

Recently, researchers at the Improbable AI Lab and MIT have put forward a proposed system that could overcome these issues. They have developed what they call the everyday finger, which is a robotic finger that was designed to be very close in size and capabilities to the human hand. This was achieved with the help of a novel actuator design, but there are still trade-offs to be made. As the name implies, the fingers are designed for common, everyday tasks. They may not be up to the task when it comes to more extreme human capabilities.

This innovation was enabled by the appearance of miniaturized, torque-dense brushless electric motors. Different motors were selected for each joint to accommodate both physical space and torque requirements. The transmission of the motors was then modified to span the full length of the fingers, with three reduction stages to keep the gears small and manage space efficiently.

The stiffness of the transmission is a critical design factor. High stiffness increases bandwidth but also raises the torque during impact, which requires stronger (and thus larger) transmissions. Conversely, lower stiffness improves impact resistance but reduces bandwidth. To reach the desired low stiffness for sustaining impacts, a spring is embedded inside one of the gears in the transmission. This integration helps maintain the size requirements while achieving the necessary mechanical properties.

Finally, a 4-bar linkage was included between the finger joints. This made it possible to mimic the natural curling motion of human fingers.

To test their approach, a two-fingered robot was created and put through a series of experiments. These experiments focused on everyday tasks, like putting away dishes and picking up fragile objects. The results of all of the tests were very favorable, demonstrating that this new style of robotic finger has the potential to make robots more human-like. Future household robots may ultimately benefit from a technology very much like this one.