It’s not easy to give a robot a sense of touch
The sense of touch is generally measured by a sensor that can translate a pressure upon it into a small electrical signal.
We have robots that can walk, see, talk and hear, and manipulate objects in their robotic hands. There’s even a robot that can smell.
But what about a sense of touch? This is easier said than done and there are limitations to some of the current methods being looked at, but we’re developing a new technique that can overcome some of those problems.
For humans, touch plays a vital role when we move our bodies. Touch, combined with sight, is crucial for tasks such as picking up objects – hard or soft, light or heavy, warm or cold – without damaging them.
In the field of robotic manipulation, in which a robot hand or gripper has to pick up an object, adding the sense of touch could remove uncertainties in dealing with soft, fragile and deformable objects.
The quest for smart skin
Quantifying touch in engineering terms not only requires the precise knowledge of the amount of external force applied to a touch sensor, but you also need to know the force’s exact position, its angle, and how it will interact with the object being manipulated.
Then there is the question about how many of these sensors a robot would need. Developing a robot skin that could contain hundreds or even thousands of touch sensors is a challenging engineering task.
Understanding the physical mechanisms of touch sensing in the biological world provides great insights when it comes to designing the robotic equivalent, a smart skin.
But a significant barrier for the development of smart skin is the electronics required.
Human skin has a multitude of sensors.
Everyday force and touch measurement
The sense of touch is generally measured by a sensor that can translate pressure into a small electrical signal. When you use a digital scale to weigh yourself or measure out ingredients in your kitchen, the scales are probably using a piezoelectric transducer.
This is a device that turns a force into electricity. The tiny electrical current from the transducer is then run through wires to a small microchip that reads the strength of the current, converts that into a meaningful weight measurement, and displays it on a screen.
Despite being able to sense different levels of force, these electronic devices have several limitations that make then impractical for smart skin. In particular, they have a relatively slow response time to the force.
There are other types of touch sensors based on a material changing its other electric characteristics, such as capacitance or resistance. Your mobile phone screen may have this technology built in, and if you use a trackpad on your computer it will certainly use touch sensors.
Soft and flexible force sensing
There has been great progress in recent years in making touch sensors that can be embedded into soft and flexible materials. This is exactly what we need for smart skin.
But many of these developments completely fail (due to the sensing type) in the presence of moisture. (Have you ever tried a wet finger on your smart phone’s touch screen?)