In the context of robotic actuators, the term torque density refers to how much torque the actuator is able to produce per unit weight or unit volume. The term can be applied to the actuator as a whole or separately to the motor or gearbox that is contained within the actuator.
Why should we be interested in torque density? Because the torque densities of a robot’s components can limit nearly every facet of a robot’s performance.
This can be easily understood by imagining one’s own body. Suppose, for example, one-kilogram weight bands were to be placed around each of our wrists. We could probably still reach our arms as high as we could before or move them as quickly as we could before, but we would easily see that much more energy is required to do so. We could now further imagine that additional weight bands are placed around our elbows in our shoulders. We’ve now effectively simulated the impact of decreasing the torque density of each of our joints in those areas by a large factor. Can we still function as we did before? Perhaps, but not very comfortably.
In the next few posts we will explore in more detail how torque density impacts robot speed, robot reach, and useful life and how all of these, in turn, roll up to affect the useful life, and hence ROI, of a robot.