(This is a small piece of a larger project I have been working on. Read the About Tactus page for an overview and stay tuned for more updates!)
As the main focus of most haptics companies, force feedback is essential to our sense of touch in the virtual world. It is what gives virtual objects physicality and presence. By pulling back against a user’s fingers, a haptic glove can simulate the shape and function of objects in the hand. Many haptic gloves do this with pneumatics or servo motors. Pneumatics are incredibly strong and accurate, but a pneumatic system does not fit on your hand. This means having a giant box next to you that contains an air compressor and a giant valve array. Servo motors are easy to use and can track position well but are limited in their force feedback capabilities. In addition, the bulk of a servo-based system means that these gloves are usually restricted to one degree of freedom per finger.
At Tactus, we are developing tiny, force feedback modules called Tensors.
These are similar to servos but are specifically designed and programmed for use with haptics. This means that their form factor, actuator motion type, speed, and controls are all completely different and optimized for haptics.
Tensors are small. The smallest common servos have about an 11 cm³ volumetric footprint while Tensors are half that size at 5.5 cm³. This small size allows Tensors to be used in almost any imaginable position on the glove, whether that is on the back of the hand or even mounted directly to a finger. In addition, Tensors were built with people in mind. While the larger, more utilitarian, blocky form of a servo matches robots well, humans are sleek and made up of organic shapes. Tensors are thin and almost finger-like, matching the design of the human hand. Because of this, they integrate naturally with our bodies and allow for a much higher actuator density, much like our muscles.
Tensors are linear actuators, just like our muscles. While our joint movements are rotational, muscles are not. In order to smoothly integrate technology with the human body, we have to match its movements. This means that actuator motion must be more natural, allowing actuators to work well with (or, in the case of haptics, against) the evolutionarily refined human body.
Tensors are fast. With a gear ratio and motor choice suited for high-frequency actuation, they are built to race right along with a user’s hands. Normal servos do not prioritize quickness and require bulky external gear chains to increase speed. For haptics, speed is key because latency and sluggish controls can ruin the magic that the technology is designed to create.
Finally, Tensors are smart. Really smart. Normal servos run a series of controls algorithm to precisely change their position. Tensors have this positional control but go way beyond that. Through current modulation and current draw measurement as well as positional and voltage control, they know everything happening at the tip of your finger. Carefully tuned algorithms give Tensors access to position, velocity, acceleration, and force control and measurement. This is where Tensors truly excel. With all of this control and data, they have complete command over touch sensation and can simulate almost any object.
Through an innovative form factor, specialized linear actuation, fast response times and intelligent control algorithms, Tensors have the ability to change haptic interaction.
The real magic comes when two Tensors work together.
Due to space constraints, tetherless haptic technologies have mostly been limited to a single degree of freedom per finger. This is analogous to having one muscle to control each finger. As anyone who uses sign language could tell you, this couldn’t be further from the truth. The human hand has 14 joints and 34 muscles to control them with. Because of this, current haptic technologies can only access a fraction of the interactions that your hands are capable of.
Most haptic gloves focus on flexion, the most common and useful motion we do with our hands. They do this by running a single cable down the back of the finger, pulling back to simulate force on the fingertip. However, flexion of each finger is controlled not by one, but by two muscles. One flexes the lowest joint on your finger (the MCP), essentially bending from the palm. The other muscle flexes the other two joints (PIP and DIP). Tensors are small enough that we can place one on top of your finger, right above the MCP. With another mounted directly behind it on the back of your palm, the Tensors mirror their respective muscles. By matching the dexterity of your hand, Tactus can simulate the exact force of any flexion-based interaction. This is a process called force-vectoring: controlling not just the intensity of forces (as most haptic gloves do), but their exact direction as well.
With complete positional and force control over the entirety of each finger, Tensors will be able to create more realistic force feedback than any other system on the market.