This is the fourth and final post in our series on the basics of haptic technology and perception. Subscribe to our newsletter to get these delivered straight to your inbox.
Force feedback: the last piece of the puzzle
All three of the sensory channels we have talked about so far – tactile, vibrotactile, and thermal – are cutaneous. That is, they are perceived by sensory organs in the skin, but our skin doesn’t have a monopoly on haptic perception. We also have similar sensory organs in our muscles and ligaments that are sensitive to forces acting on the musculoskeletal system. It’s these receptors that are responsible for the perception of force feedback.
Real interactions usually involve a combination of cutaneous feedback and force feedback. When you touch an object, interaction forces are transmitted through your skin into your musculoskeletal system. Light touch may only be perceptible as cutaneous feedback, as the forces on your musculoskeletal system are too small to be noticeable, but most interactions involve a subtle interplay of both cutaneous feedback and force feedback.
Force feedback is important in perception of gross shape, weight, and impact forces. It’s also critical for locomotion – walking, running, etc. Tactile feedback from the soles of your feet has a role in these activities as well, but force feedback is the dominant sensory channel.
A different kind of haptic device
Force feedback devices tend to look very different than cutaneous devices. As discussed in our previous posts, cutaneous devices fundamentally consist of an array of small “pixels” that apply mechanical or thermal energy to the skin. On the other hand, force feedback devices move with a user and apply forces to whole body segments, like a finger or an arm. This means they need to be capable of producing much larger movements and forces than cutaneous devices. A good force feedback device will move with a user through as much of their range of motion as possible. It will also minimize undesirable forces (i.e. from the weight or friction of the device), and match forces from virtual objects as closely as possible when a user is touching them.
There are two types of force feedback devices: biomimetic devices and non-biomimetic devices. Biomimetic devices move like the human body; non-biomimetic devices don’t. For example, a biomimetic arm force feedback device would probably have a recognizable wrist, elbow, and shoulder; a non-biomimetic arm force feedback device might look completely different than a human arm. In general, biomimetic devices are more capable, but they need to be sized to fit each user and they tend to be more difficult to design.
One other important distinction is between resistive and active devices. Resistive devices use brakes to restrict a user’s motion. Active devices use motors to both restrict a user’s motion and actively move their body around. Active devices can simulate a wider range of interactions, but they generally need to be more powerful than passive devices, and are more difficult to control.
Our HaptX™ Skeleton is a lightweight exoskeleton that can deliver full-body force feedback. HaptX Skeleton is a predominantly biomimetic design that fits tight to the body and can move with a user through virtually their full range of motion. It uses a hybrid active/resistive design to accurately reproduce a wide range of virtual interactions in a compact, lightweight form factor. Combining HaptX Skeleton’s force feedback with the high-fidelity cutaneous feedback of HaptX brings VR experiences to a whole new level of realism.
That’s it for this series, but we’ve only just begun to explore the exciting world of haptics. To get future posts delivered straight to your inbox, subscribe to our newsletter. Thanks for reading!